style(conf): enable sphinx-copybutton

[cshilwant]

Add sphinx-copybutton, a small sphinx extension to add a "copy" button to code blocks.

Fixes https://github.com/TexasInstruments/processor-sdk-doc/issues/25

[cshilwant]

@StaticRocket I see the docker.yml will get triggered once we integrate this PR but what if a requirement added by developer in requirements.txt doesn't exist or a typo that get's missed out?

Should there be a workflow to just build the docker image if there's a change in requirements.txt or docker/* ?

[cshilwant]

Sample preview with this commit

[StaticRocket]

@StaticRocket I see the docker.yml will get triggered once we integrate this PR but what if a requirement added by developer in requirements.txt doesn't exist or a typo that get's missed out?

Should there be a workflow to just build the docker image if there's a change in requirements.txt or docker/* ?

I mean, I can add one pretty quickly if we really want to check everything automatically.

[StaticRocket]

Nitpick: Extension ordering should prioritize native extensions before listing externals.

[cshilwant]

Nitpick: Extension ordering should prioritize native extensions before listing externals.

@StaticRocket Updated the PR!