Improve DataChannel.Detach() docstring

[WofWca]

Description

It wasn't clear (at least to me)
what "idiomatic API" it's referring to.

But, judging from the data-channels-detach example comments,
this is what it's made for.

webrtc/examples/data-channels-detach/main.go

Line 4 in f29ef99

// data-channels-detach is an example that shows how you can detach a data channel. This allows direct access the underlying [pion/datachannel](https://github.com/pion/datachannel). This allows you to interact with the data channel using a more idiomatic API based on the `io.ReadWriteCloser` interface.

Reference issue

None.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.64%. Comparing base (233526d) to head (d339643).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2969      +/-   ##
==========================================
- Coverage   77.66%   77.64%   -0.02%     
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  Files          89       89              
  Lines       10517    10517              
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- Hits         8168     8166       -2     
- Misses       1856     1857       +1     
- Partials      493      494       +1     

Flag	Coverage Δ
go	79.19% <ø> (-0.03%)	⬇️
wasm	63.56% <ø> (ø)

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[WofWca]

The commit linter thing probably complains about the link.

[Sean-Der]

Thank you @WofWca it is very considerate of you to update these docs. Code changes usually benefit the author, but you are doing this just to teach others :)

thank you!