manage.sh: add help

manage.sh

@@ -193,7 +193,7 @@ case $1 in
     ("install")
         mode="install"
 
-        if [ -z $2 ] ; then
+        if [ -z $2 ] || [ $2 = "--help" ]; then
             echo "usage: manage.sh install [target] (source)"
             exit 1
         fi
@@ -201,6 +201,19 @@ case $1 in
         install_target=$2
         install_source=$3
 
+        ;;
+    ("help"|"--help")
+        if [ -z $2 ] ; then
+            cat <<EOF
+usage: manage.sh [command] [options]
+
+Commands:
+
+  status        View all dotfiles
+  install       Install new dotfiles
+EOF
+            exit 1
+        fi
         ;;
     *)
         echo "Unrecognized command: '$1'"