README code snippets formatted to highlight properly

[soumendrak]

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Please provide a description of the change here.

• README code snippets highlighted by indenting correctly

[codecov-commenter]

Codecov Report

Merging #1888 (69a020d) into master (90295ea) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1888      +/-   ##
==========================================
- Coverage   92.97%   92.97%   -0.01%     
==========================================
  Files          76       76              
  Lines       16389    16388       -1     
==========================================
- Hits        15237    15236       -1     
  Misses       1152     1152              

Impacted Files	Coverage Δ
tests/test_graph.py	89.88% <0.00%> (-0.04%)	⬇️
tests/test_cluster.py	98.16% <0.00%> (ø)

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[chayim]

Thank you @soumendrak for helping to improve the overall developer experience. Much obliged!