Fix grammar and punctuation issues in README documentation (#1824)

- Changed 'community built servers' to 'community-built servers'
- Fixed 'A MCP server' to 'An MCP server' throughout
- Fixed 'a AnalyticDB' to 'an AnalyticDB'
- Added missing periods to reference server descriptions
- Fixed spacing and punctuation issues

Co-authored-by: Adam Jones <[email protected]>
Co-authored-by: Claude <[email protected]>

Author: 3 people