Add MD5 hash algorithm support

[dibu28]

Summary

This PR adds MD5 hash algorithm support to the ChecksumFolder application.

Changes Made

• Added MD5 import: Added crypto/md5 import to main.go
• Updated flag help: Updated the -hash flag help text to include md5 as an available option
• Added MD5 case: Added md5 case to the hashFile function switch statement
• Updated documentation: Updated README.md to document MD5 support in the list of available algorithms

Testing

• ✅ Built the application successfully with Go 1.23.8
• ✅ Tested MD5 hash generation on sample files
• ✅ Verified MD5 hashes match system md5sum output
• ✅ Tested verification functionality with MD5 hashes
• ✅ Tested JSON output format with MD5
• ✅ Confirmed existing SHA1 functionality still works correctly
• ✅ Verified help output shows MD5 in the list of supported algorithms

Usage

Users can now use MD5 hashing with:

CheckSumFolder -dir /path/to/dir -hash md5

MD5 is now available alongside the existing hash algorithms: md5, sha1, sha256, blake2b, blake3, xxhash, xxh3, xxh128, t1ha1, t1ha2, highway64, highway128, highway256, wyhash, and rapidhash.

Backward Compatibility

This change is fully backward compatible. All existing functionality remains unchanged, and MD5 is simply added as an additional option.

@dibu28 can click here to continue refining the PR