Docs: Fix minor typos and readability in README

[yashwanth-95]

Summary:

• Fixed minor grammatical, punctuation, and terminology issues in README.rst
• Improved readability and consistency

Notes:

• This is a trivial documentation change; no issue is associated

[python-cla-bot]

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[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[picnixz]

We don't want capitalization of every word in titles (see devguide).

I have no strong opinion on the distinction between Developer Guide and Developer's Guide though devguide has a title "Python Developer's Guide" so it may be ok to update that (I would rather have "Python Developer's Guide").

[bedevere-app]

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