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 clear support-channel routing so users know where to direct SDK-specific and broader Alpaca questions.

• Adds GitHub Issues, Community Forum, and Slack badges to the README.
• Adds matching support guidance to the README and Getting Started guide.

Confidence Score: 5/5

The documentation-only changes appear safe to merge.

The new support links and routing guidance are internally consistent and introduce no identified behavioral, security, or documentation defects.

Important Files Changed

Filename	Overview
README.md	Adds support badges and clearly routes library issues, general support, and community chat to the appropriate channels.
docs/content/getting-started.md	Adds support-channel guidance consistent with the README.

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