docs: remove pip search recommendation

[cho-m]

This is no longer supported and will just error with:

ERROR: XMLRPC request failed [code: -32500]
RuntimeError: PyPI no longer supports 'pip search' (or XML-RPC search).
Please use https://pypi.org/search (via a browser) instead. See
https://warehouse.pypa.io/api-reference/xml-rpc.html#deprecated-methods
for more information.

Also use same URL that error message recommends.

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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[MikeMcQuaid]

Thanks @cho-m!