gpt-auto-generation: set a pretty description string

src/gpt-auto-generator/gpt-auto-generator.c

@@ -144,6 +144,8 @@ static int add_swap(const char *path, const char *fstype) {
 
         fprintf(f,
                 "# Automatically generated by systemd-gpt-auto-generator\n\n"
+                "[Unit]\n"
+                "Description=Swap Partition\n\n"
                 "[Swap]\n"
                 "What=%s\n",
                 path);