Add information about how to use MongoDB as database

packages/cli/README.md

@@ -12,7 +12,7 @@ is there currently not much documentation. That will hopefully change soon.
 
 To simply spin up n8n to have a look and give it spin you can simply run:
 
-```
+```bash
 npx n8n
 ```
 
@@ -26,16 +26,63 @@ You can then access n8n by opening:
 
 To fully install n8n globally execute:
 
-```
+```bash
 npm install n8n -g
 ```
 
+## Start
+
 After the installation n8n can be started by simply typing in:
-```
+
+```bash
 n8n
+# or
+n8n start
 ```
 
 
+### Start with tunnel
+
+To be able to use webhooks which all triggers of external services like Github
+rely on n8n has to be reachable from the web. To make that easy n8n has a
+special tunnel service which redirects requests from our servers to your local
+n8n instance.
+
+To use it simply start n8n with `--tunnel`
+
+```bash
+n8n start --tunnel
+```
+
+
+### Start with MongoDB as Database
+
+By default n8n uses SQLite to save credentials, past executions and workflows.
+To use MongoDB instead you can either overwrite the default configuration on
+startup like this:
+
+```bash
+n8n start \
+  --NODE_CONFIG='{\"database\":{\"type\":\"mongodb\", \"mongodbConfig\":{\"url\":\"mongodb://MONGO_USER:MONGO_PASSWORD@MONGO_SERVER:MONGO_PORT/MONGO_DATABASE\"}}}'"
+```
+
+Or you can provide a custom configuration file by copying the default
+configuration file [(config/defaults.ts)](config/default.ts) and then set the
+path to it as environment variable `NODE_CONFIG_DIR`.
+
+For example like this:
+```bash
+export NODE_CONFIG_DIR=/path-to-my-config
+```
+
+In the file change then the
+setting under `database.type` from `sqlite` to `mongodb` and adjust the Mongo
+connection URL  `database.mongodbConfig` accordingly.
+
+
+n8n will then read your custom configuration and use MongoDB instead.
+
+
 ## License
 
 [Apache 2.0 with Commons Clause](LICENSE.md)