Add xs storage

docker-compose-generator/docker-fragments/opt-save-storage-xs.yml

@@ -0,0 +1,8 @@
+version: "3"
+
+services:
+  bitcoind:
+    environment:
+      # If you don't use Lightning Network, use opt-save-store-xxs instead
+      # This save about 3 months of block, your lightning node won't be able to see channel created 3 months since the time you start it.
+      BITCOIN_EXTRA_ARGS: prune=25000