Create chmod.md

loosely based on the proposal at #140

pages/common/chmod.md

@@ -0,0 +1,23 @@
+# chmod
+
+> Change the access permissions of a file or directory
+
+- Give the (u)ser who owns a file the right to e(x)ecute it
+
+`chmod u+x {{file}}`
+
+- Give the user rights to (r)ead and (w)rite to a file/directory
+
+`chmod u+rw {{file}}`
+
+- Remove executable rights from the (g)roup 
+
+`chmod g-x {{file}}`
+
+- Give (a)ll users rights to read and execute
+
+`chmod a+rx {{file}}`
+
+- Give (o)thers (not in the file owner's group) the same rights as the group
+
+`chmod o=g {{file}}`