Adds global update function

Adds update docs

README.md

@@ -84,6 +84,16 @@ packages in the correct order. Additionally, you can specify
 individual package names after the repository name if you only wish to
 build certain packages. 
 
+Update packages:
+
+    ./arch-ppa update [optional package names]
+	
+The update command will download new PKGBUILDs for the specified
+packages (or all if not specified.) The update will complain if you
+haven't added the existing packages to a git repository or have
+uncommited changes. Always review changes to PKGBUILD files before
+committing them. That's the point of this thing. Use `git diff src`.
+
 The repository directory can be listed in your `/etc/pacman.conf` like this:
 
     [ryan]

arch-ppa

@@ -40,6 +40,7 @@ install_system_deps() {
 	}
 	pkg_dep devtools
 	pkg_dep git
+	pkg_dep findutils
     )
 }
 
@@ -137,10 +138,17 @@ update() {
     # Update a package and it's dependencies from the AUR
     (
 	set -e
-	if [ ! -d $basedir/src/$1 ]; then
-	   echo "No package called $1 found in src"
+	if [ "$#" -eq 0 ]; then
+	    cd $basedir/src
+	    update *
+	    return
+	fi
+	for pkg in "$@"; do
+	    if [ ! -d $basedir/src/$pkg ]; then
+		echo "No package called $pkg found in src"
 		return 1
 	    fi
+	done
 	for pkg in "$@"; do
 	    check_in_git() {
 		(