Fix issue #8: Multi path input for output compilation

[chand1012]

This pull request fixes #8.

The issue has been successfully resolved. The PR modified the git2gpt tool to accept multiple repository paths as input arguments, allowing users to process files from different locations in a single run.

Key changes include:

1. Updated the command definition from requiring exactly one argument (cobra.ExactArgs(1)) to accepting one or more arguments (cobra.MinimumNArgs(1))
2. Modified the command's usage description to indicate multiple paths are supported
3. Added an example showing how to use multiple paths
4. Implemented a loop to process each provided repository path and combine their files into a single output
5. Created a test file (multi_path_test.go) that verifies the functionality works with multiple directories
6. Added test repositories with sample files to validate the implementation

The changes directly address the user's request to "paste all the required paths one after another" when files are spread across different folders. Now users can simply list all paths as arguments (e.g., git2gpt /path/to/repo1 /path/to/repo2) and get a combined output, eliminating the need to run git2gpt multiple times and manually merge the results.

Automatic fix generated by OpenHands 🙌