refactor: move helm README to docs/helm.md

[jsjoeio]

Moves README with helm information into docs/helm.md so that it can be rendered and read on the docs website.

Fixes #3877

[github-actions]

✨ Coder.com for PR #4035 deployed! It will be updated on every commit.

• Host: https://codercom-7l7wtkmkk-codercom.vercel.app/docs/code-server
• Last deploy status: success
• Commit: c772518
• Workflow status: https://github.com/cdr/code-server/actions/runs/1164561050

[jsjoeio]

lol @jawnsy can you tell I've never used Helm? 🤣

[jawnsy]

@jsjoeio We all have to start somewhere :)

[codecov]

Codecov Report

Merging #4035 (3d94af2) into main (e5a9df3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #4035   +/-   ##
=======================================
  Coverage   63.51%   63.51%           
=======================================
  Files          36       36           
  Lines        1872     1872           
  Branches      379      379           
=======================================
  Hits         1189     1189           
  Misses        580      580           
  Partials      103      103           

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