Use consistent commas around i.e. and e.g. (#12157)

## Summary

Only in user-facing docs -- I didn't bother with the rustdoc. (This is
in the style guide already.)

docs/guides/install-python.md

@@ -50,7 +50,7 @@ To install multiple Python versions:
 $ uv python install 3.11 3.12
 ```
 
-To install an alternative Python implementation, e.g. PyPy:
+To install an alternative Python implementation, e.g., PyPy:
 
 ```console
 $ uv python install pypy@3.10