Correct syntax highlighting in README

[touilleMan]

It seems Github no longer recognizes python3 in rst's code-block:: xxx tags.
Beside Github's python highlighting seems to accept Python3 keywords like await/async.

[codecov]

Codecov Report

Merging #18 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #18   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           7      7           
  Lines         776    776           
  Branches       59     59           
=====================================
  Hits          776    776

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[touilleMan]

(btw I just realized doing this edit from the Github website made me create a branch in the main repo instead of forking and working on my own... sorry for that 😢 )

[njsmith]

See #12 – Github never recognized python3, but pypi requires it. Github merged my patch to start accepting python3 like 2 months ago, but I guess they must still not have deployed it...? idk

[touilleMan]

but pypi requires it

Do you know if it requires it on the old pypi website, the new one or on both ?

Anyway, feel free to close this PR (and remove the related branch). I can do it myself if you prefer

[njsmith]

.. code-block:: python3 seems to be working on Github now!