Fix up postgres database support

Add a postgres service to the docker-compose file for convenience

docker/README.md

@@ -43,6 +43,13 @@ differences:
   database: "postgres://username:password@postgres/matrix-reminder-bot?sslmode=disable"
   ```
 
+  **Note:** a postgres container is defined in `docker-compose.yaml` for your convenience.
+  If you would like to use it, set your database connection string to:
+
+  ```
+  database: "postgres://postgres:matrixreminderbot@postgres/postgres?sslmode=disable"
+  ```
+
 Change any other config values as necessary. For instance, you may also want to
 store log files in the `/data` directory.
 
@@ -57,23 +64,32 @@ docker volume create \
   --opt device="/path/to/data/dir" data_volume
 ```
 
-Run the following to start the bot:
+If you want to use the postgres container defined in `docker-compose.yaml`, start that
+first:
+
+```
+docker-compose up -d postgres
+```
+
+Start the bot with:
 
 ```
 docker-compose up matrix-reminder-bot
 ```
 
-This will start the bot and log the bot's output. You can instead run the container detached
-with the `-d` flag:
+This will run the bot and log the output to the terminal. You can instead run
+the container detached with the `-d` flag:
 
 ```
 docker-compose up -d matrix-reminder-bot
 ```
 
+(Logs can later be accessed with the `docker logs` command).
+
 This will use the `matrix-reminder-bot:latest` tag from
 [Docker Hub](https://hub.docker.com/anoa/matrix-reminder-bot).
 
-If you would rather run from the checked out code, you can run:
+If you would rather run from the checked out code, you can use:
 
 ```
 docker-compose up local-checkout

docker/docker-compose.yml

@@ -1,14 +1,16 @@
-version: '3' # specify docker-compose version
+version: '3.1' # specify docker-compose version
 
 volumes:
   # Set up with `docker volume create ...`. See docker/README.md for more info.
   data_volume:
     external: true
+  pg_data_volume:
 
 services:
   # Runs from the latest release
   matrix-reminder-bot:
     image: anoa/matrix-reminder-bot
+    restart: always
     volumes:
       - data_volume:/data
     # Used for allowing connections to homeservers hosted on the host machine
@@ -34,3 +36,12 @@ services:
     # Defaults to 127.0.0.1 and is set in docker/.env
     extra_hosts:
       - "localhost:${HOST_IP_ADDRESS}"
+
+  # Starts up a postgres database
+  postgres:
+    image: postgres
+    restart: always
+    volumes:
+      - pg_data_volume:/var/lib/postgresql/data
+    environment:
+        POSTGRES_PASSWORD: matrixreminderbot