Docs: Add links to CPython repo and tests in Sources section

Co-Authored-By: Amp <amp@ampcode.com>

Author: heikkitoivonen

docs/index.md

@@ -61,8 +61,8 @@ Found an inaccuracy or want to add content? See our [Contributing Guidelines](ht
 
 - [Python Official Documentation](https://docs.python.org/3/)
 - [TimeComplexity Wiki](https://wiki.python.org/moin/TimeComplexity)
-- CPython source code and implementation details
-- Performance testing and benchmarking
+- [CPython source code](https://github.com/python/cpython) and implementation details
+- [Performance testing](https://github.com/heikkitoivonen/python-time-space-complexity/tree/main/tests) and benchmarking
 
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