docs: minor docs fixes

[zoryamba]

1. User guide moved from https://google-cloud-rust.github.io/ to https://googleapis.github.io/google-cloud-rust. Just fixing broken links
2. Docs include directive points to wrong sample

[coryan]

/gcbrun

[coryan]

Thanks for the PR! It all looks good, I am just waiting for a second Googler to review

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.80%. Comparing base (a87fd60) to head (bbbb59e).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5370   +/-   ##
=======================================
  Coverage   97.80%   97.80%           
=======================================
  Files         222      222           
  Lines       46563    46563           
=======================================
+ Hits        45540    45541    +1     
+ Misses       1023     1022    -1     

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