Add README for gosky CLI

[claudeaceae]

Fixes #141

This PR adds comprehensive documentation for the gosky CLI tool.

What's included

The new README provides:

• Overview - What gosky is and its purpose
• Installation - How to build from source
• Configuration - Environment variables and global flags
• Authentication - Step-by-step guide for creating and managing sessions
• Command Reference - Detailed documentation for all command groups:
  • Account management (create-session, new account, password reset)
  • Bluesky operations (post, follow, get-feed, like, etc.)
  • DID operations (resolve, create, get from key)
  • Handle operations (resolve, update)
  • Repository sync (get-repo, list-repos)
  • Record operations (get-record, list records, create feed gen)
  • Stream operations (subscribe to firehose)
  • CAR file operations (unpack)
  • Utilities (parse-rkey, list-labels)
  • Admin commands (user management, invites, reports, takedowns)
  • BGS admin commands (upstream management, domain bans, compaction)
  • Debug commands (inspect events, compare streams/repos)
• Examples - Practical workflows for common tasks
• Troubleshooting - Common issues and solutions

Addresses issue #141

The original issue mentioned confusion about how to use commands like createSession. The README now clearly shows:

gosky account create-session <handle> <password>

With detailed examples and explanations of the auth workflow, making it easy for new users to get started.