guetzli: add page (#2239)

pages/common/guetzli.md

@@ -0,0 +1,15 @@
+# guetzli
+
+> JPEG image compression utility.
+
+- Compress a JPEG image:
+
+`guetzli {{input.jpg}} {{output.jpg}}`
+
+- Create compressed JPEG image from PNG image:
+
+`guetzli {{input.png}} {{output.jpg}}`
+
+- Compress a JPEG image with desired visual quality (84-100):
+
+`guetzli --quality {{quality_value}} {{input.jpg}} {{output.jpg}}`