[25 MRG] CONTRIBUTING.md + good-first-issue path #18

Bounty: 25 MRG

Write CONTRIBUTING with setup, tests, claim flow.

Acceptance

• File + README link

Claim (MergeOS MRG)

1. Star https://github.com/mergeos-bounties/PlantGuide and https://github.com/mergeos-bounties/mergeos
2. Comment on this issue: I claim this bounty
3. Comment on MergeOS Claim Token #1 with a link to this issue
4. Open a PR to PlantGuide (public product repo) with Fixes #<this-issue>

Policy: docs/BOUNTY.md

Important

Work lands on https://github.com/mergeos-bounties/PlantGuide.

Payout

Maintainer reviews PR → merge on PlantGuide → MRG credit on MergeOS ledger to github:<author> (25/50/100/200 scale).