Add Smithery CLI Installation Instructions & Badge

[calclavia]

This PR makes two changes to the README.

1. Adds installation instructions to automatically install Text Editor Server for Claude Desktop using Smithery CLI. This makes it easier for users to install the MCP.
2. Adds a badge to show the number of installations from Smithery.

Let me know if any tweaks have to be made!

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.24%. Comparing base (176c1c8) to head (31816d4).

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Additional details and impacted files

@@           Coverage Diff           @@
##             main       #3   +/-   ##
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  Coverage   93.24%   93.24%           
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  Files          12       12           
  Lines         577      577           
  Branches       67       67           
=======================================
  Hits          538      538           
  Misses         24       24           
  Partials       15       15           

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