docs: fix more typos [skip-ci]

Author: randy408

docs/migrate-libpng.md

@@ -169,7 +169,7 @@ Some decode flags may affect the final image but never the size or the layout of
 
 ## Adding transparency
 
-This can be achieved by specifiying an output format with an alpha channel such as `SPNG_FMT_RGBA8` and the `SPNG_DECODE_TRNS` decode flag.
+This can be achieved by specifying an output format with an alpha channel such as `SPNG_FMT_RGBA8` and the `SPNG_DECODE_TRNS` decode flag.
 
 ```c
 ret = spng_decode_image(ctx, out, len, SPNG_FMT_RGBA8, SPNG_DECODE_TRNS);
@@ -178,7 +178,7 @@ ret = spng_decode_image(ctx, out, len, SPNG_FMT_RGBA8, SPNG_DECODE_TRNS);
 Note that using `SPNG_DECODE_TRNS` does not result in an error if the image does not have a tRNS chunk or
 is not applicable for the PNG format/output format combination, in those cases the flag is ignored.
 
-The `png_set_tRNS_to_alpha()` function applies a transforms which
+The `png_set_tRNS_to_alpha()` function applies a transform which
 adds an alpha channel of the same bit depth if a tRNS chunk is present.
 It also implicitly converts indexed color images to 8-bit RGB,
 1/2/4-bit grayscale images to 8-bit grayscale and also adds an alpha channel