📚 Add n8n documentation page

docs/database.md

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+# Database
+
+By default, n8n uses SQLite to save credentials, past executions, and workflows.
+n8n however also supports MongoDB and PostgresDB.
+
+
+## MongoDB
+
+!> **WARNING**: Use Postgres if possible! Mongo has problems with saving large
+   amounts of data in a document and causes also other problems. So support will
+   may be dropped in the future.
+
+To use MongoDB as database you can provide the following environment variables like
+in the example bellow:
+ - `DB_TYPE=mongodb`
+ - `DB_MONGODB_CONNECTION_URL=<CONNECTION_URL>`
+
+Replace the following placeholders with the actual data:
+ - MONGO_DATABASE
+ - MONGO_HOST
+ - MONGO_PORT
+ - MONGO_USER
+ - MONGO_PASSWORD
+
+```bash
+export DB_TYPE=mongodb
+export DB_MONGODB_CONNECTION_URL=mongodb://MONGO_USER:MONGO_PASSWORD@MONGO_HOST:MONGO_PORT/MONGO_DATABASE
+n8n start
+```
+
+
+## PostgresDB
+
+To use PostgresDB as database you can provide the following environment variables
+ - `DB_TYPE=postgresdb`
+ - `DB_POSTGRESDB_DATABASE` (default: 'n8n')
+ - `DB_POSTGRESDB_HOST` (default: 'localhost')
+ - `DB_POSTGRESDB_PORT` (default: 5432)
+ - `DB_POSTGRESDB_USER` (default: 'root')
+ - `DB_POSTGRESDB_PASSWORD` (default: empty)
+
+
+```bash
+export DB_TYPE=postgresdb
+export DB_POSTGRESDB_DATABASE=n8n
+export DB_POSTGRESDB_HOST=postgresdb
+export DB_POSTGRESDB_PORT=5432
+export DB_POSTGRESDB_USER=n8n
+export DB_POSTGRESDB_PASSWORD=n8n
+
+n8n start
+```
+
+## SQLite
+
+The default database which gets used if no other one is defined.
+
+The database file is located at:
+`~/.n8n/database.sqlite`
+
+
+## Other Databases
+
+Currently, only the above databases are supported. n8n uses internally
+[TypeORM](https://typeorm.io) so adding support for the following databases
+should not be too much work:
+
+ - CockroachDB
+ - MariaDB
+ - Microsoft SQL
+ - MySQL
+ - Oracle
+
+If you can not use any of the currently supported databases for some reason and
+you can program, you can simply add support by yourself. If not you can request
+that support should be added here:
+
+[https://community.n8n.io/c/feature-requests/cli](https://community.n8n.io/c/feature-requests/cli)