Update source.sh script and add check-version.sh script

check-version.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# Gitlab repository
+REPO="xdg/startup-notification"
+
+# Replace slash with URL encoded representation
+REPO=$(echo "$REPO" | sed 's|/|%2F|g')
+
+# Get tag name using Gitlab Rest API
+TAG_NAME=$(curl -s -L https://gitlab.freedesktop.org/api/v4/projects/"$REPO"/repository/tags | jq -r '.[0].name')
+
+# Trim prefix
+VERSION=${TAG_NAME//STARTUP_NOTIFICATION_/}
+
+# Replace '_' with '.'
+VERSION=${VERSION//_/.}
+
+echo "$VERSION"