docs: add documentation for external database configuration (#4707)

* Add documentation for configuring external databases with Langflow

* Update title in configuration documentation to 'External Database Configuration'

* Update PostgreSQL configuration docs to include .env file usage instructions

* more-context

* fix: improve clarity in instructions for starting services in custom database configuration

---------

Co-authored-by: Mendon Kissling <59585235+mendonk@users.noreply.github.com>

docs/docs/Configuration/configuration-custom-database.md

@@ -0,0 +1,76 @@
+---
+title: Configure an external PostgreSQL database
+sidebar_position: 8
+---
+Langflow's default database is [SQLite](https://www.sqlite.org/docs.html), but you can configure Langflow to use PostgreSQL instead.
+
+This guide will walk you through the process of setting up an external database for Langflow by replacing the default SQLite connection string `sqlite:///./langflow.db` with PostgreSQL.
+
+## Prerequisite
+
+* A [PostgreSQL](https://www.pgadmin.org/download/) database
+
+## Connect Langflow to PostgreSQL
+
+To connect Langflow to PostgreSQL, follow these steps.
+
+1. Find your PostgreSQL database's connection string.
+It looks like `postgresql://user:password@host:port/dbname`.
+For example, if you started PostgreSQL with this Docker command:
+
+```
+docker run --name some-postgres -e POSTGRES_PASSWORD=mysecretpassword -d -p 5432:5432 postgres
+```
+
+Your connection string would be `postgresql://some-postgres:mysecretpassword@localhost:5432/postgres`.
+
+2. Create a `.env` file for configuring Langflow.
+```
+touch .env
+```
+
+3. To set the database URL environment variable, add it to your `.env` file:
+```plaintext
+LANGFLOW_DATABASE_URL="postgresql://user:password@localhost:5432/dbname"
+```
+
+:::tip
+The Langflow project includes a [`.env.example`](https://github.com/langflow-ai/langflow/blob/main/.env.example) file to help you get started.
+You can copy the contents of this file into your own `.env` file and replace the example values with your own preferred settings.
+Replace the value for `LANGFLOW_DATABASE_URL` with your PostgreSQL connection string.
+:::
+
+4. Run Langflow with the `.env` file:
+```bash
+langflow run --env-file .env
+```
+
+5. In Langflow, create traffic by running a flow.
+6. Inspect your PostgreSQL deployment's tables and activity.
+You will see new tables and traffic created.
+
+## Example Langflow and PostgreSQL docker-compose.yml
+
+The Langflow project includes a [`docker-compose.yml`](https://github.com/langflow-ai/langflow/blob/main/docker_example/docker-compose.yml) file  for quick deployment with PostgreSQL.
+
+This configuration launches Langflow and PostgreSQL containers, with Langflow pre-configured to use the PostgreSQL database. Customize the database credentials as needed.
+
+To start the services, navigate to the `/docker_example` directory, and then run `docker-compose up`.
+
+```yaml
+services:
+  langflow:
+    image: langflow-ai/langflow:latest
+    environment:
+      - LANGFLOW_DATABASE_URL=postgresql://user:password@postgres:5432/langflow
+    depends_on:
+      - postgres
+
+  postgres:
+    image: postgres:15
+    environment:
+      - POSTGRES_USER=user
+      - POSTGRES_PASSWORD=password
+      - POSTGRES_DB=langflow
+```
+