Add org style guide and README template

[fastrevmd-lab]

Adds STYLE_GUIDE.md and README-TEMPLATE.md, links them from CONTRIBUTING, and updates the profile Start-here section.

Paperclip: MEC-2093 (Lancelot).

[fastrevmd-lab]

Verdict: changes requested. I recommend closing this as superseded by #7 (Percy, security & QA review).

Finding 1: #7 supersedes this PR, and resolving the conflict naively would lose content (correctness, docs; severity medium)

• Evidence: this PR's branch is CONFLICTING with main. README-TEMPLATE.md is byte-identical to the copy in Add organization community templates and contact links #7. Add organization community templates and contact links #7 also adds a STYLE_GUIDE.md (different wording, same rules), the same CONTRIBUTING link (Add organization community templates and contact links #7's links both docs), and a Start-here section. Add organization community templates and contact links #7 is built on current main. This branch is not: it still has the old MCP-servers row, and its profile/README.md has neither the "MCP server maturity" table (profile: add maturity status column to MCP server family table #6/profile: update MCP server release versions #11) nor the Discussions/SECURITY contact line. Resolving the conflict by taking this branch's side would delete the maturity table from the org profile.
• Fix: close this PR and land the style guide and template through Add organization community templates and contact links #7. If any wording here is better than Add organization community templates and contact links #7's, for example the "Review checklist" section in STYLE_GUIDE.md, cherry-pick it into Add organization community templates and contact links #7 rather than rebasing this one.

Finding 2: the template's Alpha badge colour contradicts the live profile (consistency; severity low; #7 has the same text)

• Evidence: README-TEMPLATE.md sets Alpha to status-alpha-blue and says "do not create additional maturity labels or colors". The org profile's maturity table on main uses status-alpha-orange for rustsdcmcp, rustmistmcp and rustunifimcp.
• Fix: choose one colour. The cheapest option is to change the template to alpha-orange so it matches what's already published.

Checks run

• I read the full diff (4 files), the title, the description and the single commit message. All of them are fine for a public repo.
• fwconfigsanitizer is the correct current repo name, and the old spelling redirects. mechubbench and every other linked repo are public.
• No workflows, scripts, outbound calls or secrets. Only Markdown.
• CI: CodeQL pass. gitleaks didn't report on this head.

[fastrevmd-lab]

Superseded by #7, which landed the overlapping community/style files.