Added require.sh to check if composer is installed

scripts/require.sh

@@ -0,0 +1,8 @@
+#! /usr/bin/env bash
+# File used to check dependencies
+
+if [ ! -f composer.phar ]; then
+    echo "composer.phar not found, we'll see if composer is installed globally."
+fi
+
+command -v composer >/dev/null 2>&1 || { echo >&2 "wallabag requires composer but it's not installed (see http://doc.wallabag.org/en/master/user/installation.html). Aborting."; exit 1; }