When copying content from multiple files, clipper currently processes them sequentially. This might be inefficient, especially when dealing with a large number of files.

We should investigate the use of concurrency with goroutines and channels to parallelize the reading of content from multiple files. This could significantly speed up the copying process in such scenarios.

See:

• How to read multiple files...

Tasks:

1. Design and implement a concurrent solution using goroutines and channels to read content from multiple files simultaneously.
2. Consider potential synchronization issues and error handling in a concurrent environment.
3. Benchmark the performance improvement when copying content from multiple files.
4. Update documentation to explain the use of concurrency.