Add patch command.

pages/common/patch.md

@@ -0,0 +1,15 @@
+#patch
+
+> Patch a file or files with a diff file.
+
+- apply a patch
+
+`patch < {{patchfile}}.diff`
+
+- apply a patch to current directory
+
+`patch -p1 < {{patchfile}}.diff`
+
+- reverse a patch
+
+`patch -R < {{patchfile}}.diff`