Docs: move documentation to README

[ohmyfelix]

What changed

• Moved the package documentation from .docs/README.md into the root README.md.
• Kept the Contributte badge/contact scaffold and added a concise package intro.
• Removed the documentation wrapper and fixed moved relative template links.

Why

Refs contributte/contributte#75

Testing

• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.38%. Comparing base (81e9f52) to head (dde6601).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #73   +/-   ##
=======================================
  Coverage   96.38%   96.38%           
=======================================
  Files          17       17           
  Lines         249      249           
=======================================
  Hits          240      240           
  Misses          9        9           

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