docs: add support channel routing to README and getting started

[carlostasada]

Point users to GitHub Issues for SDK bugs/requests, and to the Forum and Slack for account, API, and community help.

[greptile-apps]

Greptile Summary

Adds support-channel guidance so users can route CLI issues to GitHub and broader Alpaca questions to community channels.

• Adds Forum and Slack badges near the README header.
• Adds a Support section linking to GitHub Issues, the Alpaca Community Forum, and Slack.

Confidence Score: 5/5

The documentation-only change appears safe to merge.

The new support destinations are consistent with existing repository references, and no broken routing, rendering, or repository-rule violation was established.

Important Files Changed

Filename	Overview
README.md	Adds consistent, correctly targeted support links and community badges without introducing an actionable documentation defect.

_{Reviews (1): Last reviewed commit: "docs: add support channel routing to REA..." | Re-trigger Greptile}