docs: update README usage to match actual fpack/funpack CLI behavior

README.md

@@ -14,10 +14,21 @@ build.bat debug release tools    # Windows
 ## Usage
 
 ```bash
-fpack output.fpk assets/
+fpack [-o output.fpk] [-p] [-q] [-v] input_dir
-funpack output.fpk [unpacked/]   # dir defaults to "output" if omitted
+funpack [-d output_dir] [-l] [-p] [-q] [-v] input.fpk
 ```
 
+`fpack` walks `input_dir` recursively (skipping dotfiles) and writes an
+archive. If `-o` is omitted, the output name is derived from the input
+directory's basename plus `.fpk` (e.g. `assets/` -> `assets.fpk`).
+
+`funpack` extracts (or, with `-l`, lists) the entries in `input.fpk`. If
+`-d` is omitted, the output directory is derived from the archive's
+basename with `.fpk` stripped (e.g. `assets.fpk` -> `assets/`).
+
+Common flags: `-p` show progress, `-q` suppress the summary line, `-v`
+print each entry as it's processed.
+
 ```c
 #include <fpk/fpk.h>