Update Documentation Link on Pypi Page

[johnjameswhitman]

The Pypi package page for google-cloud-language v0.25.0 links to the wrong Documentation site (might just be out of step with head).

• Is: https://googlecloudplatform.github.io/google-cloud-python/stable/language-usage.html
• Should be: https://googlecloudplatform.github.io/google-cloud-python/stable/language/usage.html

I couldn't find where this is versioned, otherwise would have submitted a PR.

[dhermes]

Thanks for filing @johnjameswhitman! I fixed this "broken link" issue in #3631. Unfortunately, AFAIK there is current (pypa/packaging-problems#97) no way to edit package metadata (which includes the README), so that version is "stuck" with a bad link.

The real fix going forward is to have fully versioned docs (tough right now with our UBER-package) and to link in the README on PyPI to the versioned docs.

[lukesneeringer]

I am going to go ahead and close this. I agree with the description of the problem, and the fix, but tracking this as a separate line item probably is not going to be all that useful.

@johnjameswhitman Thank you for reporting, and we have a medium-term plan that will sort this out, even for old versions.