Document website pull request target

[JackieTien97]

Summary

• add a Website Contributions section to the root README
• state that website pull requests must use docs/dev as the base branch

Motivation

The release branch README did not tell contributors which branch receives website changes.

Impact

Contributors working from the 1.1 release branch can identify the correct base branch before opening website documentation pull requests.

Root cause

The website contribution workflow was not documented in the repository README.

Validation

• git diff --check

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.82%. Comparing base (b1ebf29) to head (92ae5cf).

Additional details and impacted files

@@           Coverage Diff            @@
##           dev/1.1     #888   +/-   ##
========================================
  Coverage    58.82%   58.82%           
========================================
  Files          420      420           
  Lines        28117    28117           
  Branches      3717     3718    +1     
========================================
  Hits         16541    16541           
  Misses       11380    11380           
  Partials       196      196           

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