colorpicker: add page (#6098)

pages/common/colorpicker.md

@@ -0,0 +1,25 @@
+# colorpicker
+
+> A minimalist X11 colorpicker.
+> Any mouse gesture except left click will exit the program.
+> More information: <https://github.com/ym1234/colorpicker>.
+
+- Launch colorpicker and print the hexadecimal and RGB value of each clicked pixel to stdout:
+
+`colorpicker`
+
+- Only print the color of one clicked pixel and then exit:
+
+`colorpicker --one-shot`
+
+- Print the color of each clicked pixel and quit when a key is pressed:
+
+`colorpicker --quit-on-keypress`
+
+- Only print the RGB value:
+
+`colorpicker --rgb`
+
+- Only print the hexadecimal value:
+
+`colorpicker --hex`