[codex] docs: clarify TSK caveat and add fork freshness badges

[DMontgomery40]

What changed

• add a prominent README note that TSS version alone is not enough to determine TSK/SecOC compatibility
• add freshness badges for the documented openpilot, sunnypilot, FrogPilot, and SatoPilot branches
• wrap the existing README table of contents in markers so a follow-up TOC sync script can manage it safely

Why

• the new note makes an easy-to-miss compatibility caveat much more obvious near the car list
• the badges give readers a quick signal for how active each recommended branch is
• the TOC markers prepare the README for a follow-up automation PR without changing the current TOC contents

Validation

• git diff --check
• verified each badge branch exists with git ls-remote --heads

[calvinpark]

I have mixed feelings about the freshness badges.

1. Keeping a list of popular forks & branches isn't the purpose of this doc. It's about stopping people from installing a known incompatible fork/branch.
2. On sunnypilot's case, they specifically prefer to guide people to use their installer, rather than a branch name. Mentions of tizi/tici/mici will confuse the newbies, whom this document is for.

But on the other hand, it's very small and doesn't look half bad.

[DMontgomery40]

Yeah I get it, just thought I'd throw it out there