pngcheck: add page (#5310)

pages/common/pngcheck.md

@@ -0,0 +1,28 @@
+# pngcheck
+
+> Print detailed information about and verify PNG, JNG, and MNG files.
+> More information: <http://www.libpng.org/pub/png/apps/pngcheck.html>.
+
+- Print a summary for an image (width, height, and color depth):
+
+`pngcheck {{image.png}}`
+
+- Print information for an image with [c]olorized output:
+
+`pngcheck -c {{image.png}}`
+
+- Print [v]erbose information for an image:
+
+`pngcheck -cvt {{image.png}}`
+
+- Receive an image from stdin and display detailed information:
+
+`cat {{path/to/image.png}} | pngcheck -cvt`
+
+- [s]earch for PNGs within a specific file and display information about them:
+
+`pngcheck -s {{image.png}}`
+
+- Search for PNGs within another file and e[x]tract them:
+
+`pngcheck -x {{image.png}}`