Support multiple file/directory arguments for all commands

- Change sum add, sum update, check, and clear to accept 1+ paths
- Update README usage examples to show multiple path support
- Add TODO section with planned future improvements

README.md

@@ -31,20 +31,20 @@ Semantic Versioning 2.0.0 is used for tags.
 ## Usage
 
 ```bash
-# add checksum & timestamp xattrs to every regular file under DIR
-attrsum sum add DIR
+# add checksum & timestamp xattrs to every regular file under one or more paths
+attrsum sum add DIR1 DIR2 file.txt
 
 # update checksum only when file mtime is newer than stored sumtime
-attrsum sum update DIR
+attrsum sum update DIR1 DIR2
 
 # verify checksums, stop on first error
-attrsum check DIR
+attrsum check DIR1 DIR2
 
 # verify every file, reporting each result, keep going after errors
-attrsum -v check --continue DIR
+attrsum -v check --continue DIR1 DIR2
 
 # remove checksum & timestamp xattrs
-attrsum clear DIR
+attrsum clear DIR1 DIR2
 ```
 
 | xattr key                                   | meaning                        |
@@ -71,6 +71,21 @@ required.  Now you can trust a USB stick didn't eat your data.
 
 ---
 
+## TODO
+
+Future improvements under consideration:
+
+- **Quiet mode (`-q`)** — suppress all output except errors
+- **Dry-run mode (`--dry-run`, `-n`)** — show what would be done without making changes
+- **JSON output (`--json`)** — machine-readable output for scripting and integration
+- **Parallel processing (`-j N`)** — use multiple goroutines for faster checksumming on large trees
+- **Progress indicator** — show progress bar or spinner for long-running operations
+- **Summary report** — print statistics on completion (files processed, errors, bytes hashed)
+- **Read paths from stdin (`-`)** — support piping file lists, e.g. `find ... | attrsum sum add -`
+- **Exit code documentation** — formalize and document exit codes for scripting
+
+---
+
 ## Contributing
 
 * Author & maintainer: **sneak** – <sneak@sneak.berlin>