docs: correct the merge-method section against the live ruleset

[Bryan Fawcett (bryanfawcett)]

The Merge method section was wrong in both directions, and this is the
document other repos in the org are meant to copy their settings from.

It said "the org ruleset allows squash merges only". GET
/orgs/mukoko-dev/rulesets/22932468 returns
allowed_merge_methods: ["rebase"] on the pull_request rule. Rebase, not
squash.

It said "the repository-level settings in this org still leave merge-commit
and rebase switched on". Every repository checked - mukoko, mukoko-auth,
kweli, kweli-mcp, mukoko-lingo, mukoko-home, packages-ui - reports
allow_squash_merge: false, allow_merge_commit: false, allow_rebase_merge:
true, allow_auto_merge: true. The settings and the ruleset agree; the README
was the only thing disagreeing with either.

It listed required_signatures as part of the ruleset. The ruleset's rules
are deletion, non_fast_forward, required_linear_history, pull_request and
required_status_checks. There is no signature requirement, and the README now
says so explicitly so the claim does not come back.

Added, all verified against the API:

• The rest of what the pull_request rule actually does - stale reviews
  dismissed on push, review threads must resolve, unattributed changes need
  an extra approval, and required_approving_review_count is 0.
• That required_status_checks is strict, so branches must be up to date.
• That the ruleset skips sandbox-* and archive-* repositories.
• The second ruleset, enterprise-main-protection, inherited from the
  bundu-labs enterprise and currently in evaluate mode, blocking nothing.

Also:

• Documented the three workflows this repository actually ships - lint.yml,
  pr-title-lint.yml and stale.yml - with their triggers. The README described
  only lint.yml.
• Extended the reusable-workflow table. nyuchi/.github publishes 21 reusable
  workflows; the table listed five of them and read as exhaustive. It now
  covers Python, Rust, MDX docs, Docker, Terraform/OpenTofu and Solidity, and
  says plainly that the directory is the authority.
• Added the Lint badge (curls 200) and an at-a-glance line, and a licence
  section recording that no LICENSE file is committed here.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com