docs: Add note in local-mcp-server README.md recommending the use of the remote MCP server

[steve-calvert-glean]

Description

Code changes:

• Added a note in the README.md recommending the use of the remote MCP server integrated directly in Glean instead of the local MCP server, highlighting benefits such as automatic updates, better performance, and simplified configuration. This local server is now indicated as primarily for experimental and testing purposes.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Build/CI pipeline changes
• Other (please describe):

[rwjblue-glean]

Seems good! Should we also add this to the top level README? I'm just not sure why someone would use or look at this repo at all when they could use the remote MCP server in 99+% of the cases...