Add link to usage example in the documentation

[kleysc]

Closes #945

Description

This pull request adds a link to a practical example of how to interact with Lightning Network nodes using Polar as a development environment. The example is available in Spanish to support the Hispanic community.

Steps to Test

1. Open the README.md file.
2. Navigate to the "Usage Examples" section.
3. Verify the link to the example repository: lightning-polar-ejemplo

Screenshots

(Not applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (584a812) to head (4dad0bb).
⚠️ Report is 441 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #953   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          151       151           
  Lines         5498      5498           
  Branches      1105      1062   -43     
=========================================
  Hits          5498      5498           

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