Update .wav samples to use 'agbl' chunk to accomodate for vanilla's off-by-one loop end behavior (#712)

tools/wav2agb/README.md

@@ -6,9 +6,12 @@ This copy has been slightly modified from [ipatix's original implementation](htt
 2. Support reading an override "pitch" value from a custom `agbp` RIFF chunk.
    - This is needed to properly match some samples, due to float-point rounding errors when attempting to infer the pitch/sample rate from the .wav file's sample rate.
    - If the custom `agbp` chunk isn't present, it will simply use the .wav's sample rate to calculate this "pitch" value.
-3. Optionally omits trailing padding from compressed output.
+3. Support reading an override "loop end" value from a custom `agbl` RIFF chunk.
+   - This is needed to properly match vanilla samples, due their their inherent off-by-one error (the last sample is mistakenly ignored).
+   - This `agbl` chunk can be added to existing .wav files with the `--set-agbl` option (described below).
+4. Optionally omits trailing padding from compressed output.
 
-Usage: 
+Usage:
 ```
 Usage: wav2agb [options] <input.wav> [<output>]
 
@@ -24,6 +27,29 @@ Options:
 --tune <cents>           | override tuning (float)
 --key <key>              | override midi key (int)
 --rate <rate>            | override base samplerate (int)
+--set-agbl <loop-end>    | adds the custom agbl chunk to the given input .wav file
 ```
 
 Flag -c enables compression (only supported by Pokemon Games)
+
+## Adding agbl Chunk to WAV Files
+
+The `--set-agbl` option allows you to add or update the custom `agbl` chunk in a WAV file. When this option is used, `wav2agb` will output a WAV file with the agbl chunk added, rather than converting to `.s` or `.bin` format.
+
+The loop-end value can be specified as either:
+- **Positive value**: Used as an absolute sample position
+- **Negative value**: Treated as an offset from the end of the file
+
+This is useful for correcting the off-by-one loop-end error in vanilla samples. The typical fix is `--set-agbl -1`, which sets the loop-end to `(total_samples - 1)`.
+
+Example:
+```bash
+# Set agbl to (total_samples - 1), the most common case for fixing the off-by-one error
+wav2agb --set-agbl -1 input.wav
+
+# Set agbl chunk to specific sample position 12345
+wav2agb --set-agbl 12345 input.wav output.wav
+
+# If no output file is specified, the input file is modified in place
+wav2agb --set-agbl -1 input.wav
+```