docs: add community-health files (SECURITY, CODE_OF_CONDUCT, CONTRIBUTING)

[jhamon]

Theme: Discoverability & Presentation

Problem

This public repo has no SECURITY.md, CODE_OF_CONDUCT.md, or CONTRIBUTING.md, and the org pinecone-io/.github repo does not supply them as defaults (it provides only ISSUE_TEMPLATE/ and pull_request_template.md). GitHub therefore shows no security policy / code of conduct / contributing guide for the repo.

Proposed fix

Add the three files at the repo root (or .github/):

• SECURITY.md — how to report a vulnerability (private disclosure contact/process).
• CODE_OF_CONDUCT.md — standard Contributor Covenant.
• CONTRIBUTING.md — how to set up, run tests, and open a PR for this example.

Keep them short and consistent with other Pinecone example repos. If an org-wide policy is later centralized in pinecone-io/.github, these can defer to it.

Acceptance criteria

• All three files present and rendered by GitHub (security policy + code of conduct show in the repo's Community/Insights tab).
• Content is accurate for this repo (correct run/test commands in CONTRIBUTING).

Blast radius

safe

Dependencies

None.