doc: update README documentation

README.md

@@ -13,12 +13,190 @@ KM (Kanna Mapper) helps you auto-generate mapping between types and supports con
 
 Unlike other mappers, KM leverages code generation and does not use reflection, which means there are no errors during runtime, and offers much better performance than other solutions that use reflection.
 
+✔️ Doesn't use reflection
+
+✔️ Leverage fails early so nothing will generate in case of errors
+
+✔️ Configurable
+
+✔️ Different generation styles
+
+✔️ Concurrent generation
+
+## Install
+
+```
+go install github.com/khatibomar/km@latest
+```
+
+## Flags
+
+```
+Flags:
+  -config string
+        mapping configuration file (default "km.toml")
+  -debug
+        log result instead of writing to files
+```
+
 ## Usage
 
-Coming soon...
+First, create `km.toml` file, this file will hold the mapping configuration, and it's considered the root directory of the generator, which means if we have folder `folder/sub_folder/km.toml` the `sub_folder` is the root directory for mapper and you can't map things in `folder`
+
+```toml
+[settings]
+style="value"
+module="github.com/khatibomar/km/"
+path_from_module="testdata"
+
+[[mappings]]
+  [mappings.source]
+  name = "Car"
+  path = "./car/car.go"
+
+  [mappings.destination]
+  name = "CarDTO"
+  path = "./dto/car_dto.go"
+  ignore = ["Owner"]
+
+  [mappings.destination.map]
+  FactoryModel = "Model"
+
+[[mappings]]
+  [mappings.source]
+  name = "User"
+  path = "./user/user.go"
+
+  [mappings.destination]
+  name = "UserDTO"
+  path = "./dto/user_dto.go"
+```
+
+we are going to use `testdata` folder
+
+So in `settings` we set `PathFromModule` to `testdata` this setting is nothing but how we can access the config file starting from the root of the project itself, not the config.
+
+This is the tree of the `testdata` before running generation
+
+```
+  94 B    ┌─ car.go
+  94 B ┌─ car
+ 163 B │  ┌─ user.go
+ 163 B ├─ user
+ 103 B │  ┌─ car_dto.go
+ 157 B │  ├─ user_dto.go
+ 260 B ├─ dto
+ 483 B ├─ km.toml
+1000 B testdata
+```
+
+after that run `km` which will generate `km_gen.go` in the destination path.
+
+tree after generation
+
+```
+  94 B    ┌─ car.go
+  94 B ┌─ car
+ 163 B │  ┌─ user.go
+ 163 B ├─ user
+ 483 B ├─ km.toml
+ 103 B │  ┌─ car_dto.go
+ 157 B │  ├─ user_dto.go
+ 363 B │  ├─ km_gen.go
+ 623 B ├─ dto
+1363 B testdata
+```
+
+we can see that `km_gen.go` is generated in the destination path.
+
+```go
+package dto
+
+import (
+	"github.com/khatibomar/km/testdata/car"
+	"github.com/khatibomar/km/testdata/user"
+)
+
+func (dest CarDTO) FromCar(src car.Car) CarDTO {
+	dest.FactoryModel = src.Model
+	dest.Color = src.Color
+	dest.Speed = src.Speed
+	return dest
+}
+
+func (dest UserDTO) FromUser(src user.User) UserDTO {
+	dest.Name = src.Name
+	dest.Age = src.Age
+	return dest
+}
+```
+
+## Settings
+
+### Global
+
+| setting | Description |
+| -- | -- |
+| style | specify mapping style, default style is `value`  |
+| module | is the module of the repository |
+| path_from_module | how we can access the config file starting from the root of the project itself |
+
+### Source
+| setting | Description |
+| -- | -- |
+| name | name of the type  |
+| path | where can locate the type, root starts from config file |
+
+### Destination
+| setting | Description |
+| -- | -- |
+| name | name of the type  |
+| path | where can locate the type, root starts from config file |
+| ignore | fields to ignore during mapping |
+| map | map from destination to source field |
+
+## Styles
+
+| Approach                                   | Description                                                                                           | Use Case                                                                                                                                                       |
+|--------------------------------------------|-------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| pointer             | Modifies the existing instance of the destination directly.                                                      | When you want to modify the existing instance of destination without creating a new one.                                                                                |
+| value           | Creates a copy of the destination struct, modifies the copy, and returns it, leaving the original intact.   | When you want to keep the original destination struct intact and produce a modified copy.                                                                                |
+| standalone             | A standalone function that takes destination as a parameter and returns a modified version of it.         | When you want to keep the modification logic separate from the struct's methods or need more flexibility in how you apply the modification.    
+
+#### Value
+```go
+func (dest CarDTO) FromCar(src car.Car) CarDTO {
+	dest.FactoryModel = src.Model
+	dest.Color = src.Color
+	dest.Speed = src.Speed
+	return dest
+}
+```
+
+#### pointer
+
+```go
+func (dest *CarDTO) FromCar(src car.Car) {
+	dest.FactoryModel = src.Model
+	dest.Color = src.Color
+	dest.Speed = src.Speed
+}
+```
+
+#### standalone
+
+```go
+func CarDTOFromCar(dest CarDTO, src car.Car) CarDTO {
+	dest.FactoryModel = src.Model
+	dest.Color = src.Color
+	dest.Speed = src.Speed
+	return dest
+}
+```
 
 ## Upcoming
-- [ ] Adding more tests 
+- [X] Adding more tests 
 - [ ] Support for map <-> struct
-- [ ] Better documentation
+- [X] Better documentation
 - [ ] Handle conversion between types
+- [ ] Recursive mapping for complex fields