Add local caching feature to readme

[bendichter]

fix #109

I have successfully fixed issue #109 by adding comprehensive documentation for the Local Cache feature to the README.md file.

The new documentation includes:

1. Basic cache usage - Shows how to create a LocalCache instance and use it with remote files
2. Cache with LINDI files - Demonstrates using the cache when working with LINDI JSON files that reference remote data
3. How the cache works - Technical details about the SQLite backend, default cache location (~/.lindi/cache), chunk size limits (900 MB), and persistence across sessions
4. Cache benefits - Performance improvements, bandwidth reduction, and development workflow advantages

The documentation provides clear Python code examples showing how to:

• Create a local cache with default or custom directory
• Use the cache when loading remote HDF5 files
• Use the cache with LINDI JSON files
• Understand the performance benefits of repeated access

This resolves the issue by making the already-implemented cache feature discoverable and usable through proper documentation in the README.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.43%. Comparing base (8f97939) to head (882bebe).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #110   +/-   ##
=======================================
  Coverage   81.43%   81.43%           
=======================================
  Files          30       30           
  Lines        2790     2790           
=======================================
  Hits         2272     2272           
  Misses        518      518           

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[bendichter]

@magland thoughts on this?

[magland]

Looks great, thanks!