snippet: add link to uncompng.c example
diff --git a/snippet/uncompng.c b/snippet/uncompng.c
index c6b23e5..41eebcb 100644
--- a/snippet/uncompng.c
+++ b/snippet/uncompng.c
@@ -22,6 +22,9 @@
//
// It is a C port of the github.com/google/wuffs/lib/uncompng library. The
// original Go code has much more comments about the algorithmic details.
+//
+// There's an example program (using this library) at
+// https://nigeltao.github.io/blog/2025/uncompressed-png.html
#ifndef UNCOMPNG_INCLUDE_GUARD
#define UNCOMPNG_INCLUDE_GUARD
@@ -71,15 +74,18 @@
// entirety of the (data_ptr, data_len) slice. data_len will never exceed
// UNCOMPNG__DATA_LEN__INCL_MAX.
//
-// write_func should return zero for success or non-zero for failure (which is
+// It returns zero on success, a positive number (an UNCOMPNG__RESULT__ETC
+// constant) on library failures or a negative number on write_func failures.
+//
+// write_func should return zero for success or negative for failure (which is
// passed back to the uncompng__encode caller). Returning a positive number is
// not recommended, as that may clash with UNCOMPNG__RESULT__ETC values.
//
// The context argument is unused other than being an opaque value that is
// forwarded on to write_func.
//
-// Pixel data is in the (pixel_ptr, pixel_len) slice, either 1 or 4 bytes per
-// pixel depending on the pixel_format. width and height are measured in
+// Pixel data is in the (pixel_ptr, pixel_len) slice, either 1, 2, 4 or 8 bytes
+// per pixel depending on the pixel_format. width and height are measured in
// pixels. stride, the pointer difference between rows, is measured in bytes.
//
// This function is not thread-safe.
