Add PostgreSQL configuration example

.gitignore

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+# Created by .ignore support plugin (hsz.mobi)
+
+.idea

README.md

@@ -16,6 +16,7 @@ Don't forget the [Official documentation](https://ddev.readthedocs.io/en/stable/
 ## Additional services added via docker-compose.\<service\>.yaml
 * [MongoDB](docker-compose-services/mongodb/README.md)
 * [Blackfire.io](docker-compose-services/blackfire/README.md)
+* [PostreSQL](docker-compose-services/postgres/README.md)
 
 ## .ddev/web-build/Dockerfile examples to customize web container
 

docker-compose-services/postgres/README.md

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+## PostgreSQL
+
+Using PostgreSQL container with [PostGIS](https://postgis.net/) support provided by [mdillon/postgis](https://hub.docker.com/r/mdillon/postgis).
+
+### Installation
+
+1. Copy `docker-compose.postgres.yaml` to your project
+2. Copy the full `commands/postgres` directory to your project's `.ddev/commands` directory. For example `cp -r commands/postgres /.ddev/commands`
+3. *(optional)* Update your config.yaml file to support auto-import/auto-export (see below)
+
+### Connection
+
+Connect to `postgres` host/db server from within the web container with:
+
+```
+Host: postgres
+User: db
+Password: db
+Database: db
+```
+
+For external access, use the port used in your `docker-compose.postgres.yaml` and `127.0.0.1` as host.
+
+When using multiple project with PostgreSQL support, remember to update your `docker-compose.postgres.yaml` to use different ports:
+
+```
+    ports:
+      - <EXTERNAL_PORT>:5432
+``` 
+
+### Import / Export
+
+Two new `ddev` commands are provided:
+
+- `ddev pgsql_export` : Use `pg_dump` to export `db` to `.ddev/import-db/postgresql.db.sql`  
+- `ddev pgsql_import` : Use `pgsql` to import `.ddev/import-db/postgresql.db.sql` into `db` - Note that this must be executed with an empty database.
+
+Example `config.yaml` hooks configuration to automatically import/export the `db` table:
+
+```
+hooks:
+  pre-stop:
+    - exec-host: ddev pgsql_export
+  post-start:
+    - exec-host: ddev pgsql_import
+```
+
+### PostGIS
+
+The `postgres` image support `postgis`, but you will need to create the extension before using it:
+
+```
+CREATE EXTENSION IF NOT EXISTS `postgis`;
+```
+
+### TODO
+
+Future enhancements (PR's welcome here) include:
+
+* Non-volatile postgres database (store it on a docker volume like ddev's normal mariadb container does)
+* Provide interactive custom commands to interact with the `postgres` utility in the container interactively.
+* Consider changing suggested import/export hooks into "exec" hooks with "service: postgres" instead of running `ddev pg*` on the host.

docker-compose-services/postgres/commands/postgres/pgsql_export

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+#!/bin/bash
+
+## Description: Dump the postgresql database to .ddev/import-db/postgresql.db.sql
+## Usage: pgsql_export
+## Example: ddev pgsql_export
+
+mkdir -p /mnt/ddev_config/import-db && su postgres -c "pg_dump db --username=db --host=localhost --port=5432 --column-inserts > /mnt/ddev_config/import-db/postgresql.db.sql"

docker-compose-services/postgres/commands/postgres/pgsql_import

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+#!/bin/bash
+
+## Description: Load to an empty postgresql database from .ddev/import-db/postgresql.db.sql
+## Usage: pgsql_import
+## Example: ddev pgsql_import
+
+# Import via user postgres to avoid credentials prompt
+su postgres -c "psql -U db db < /mnt/ddev_config/import-db/postgresql.db.sql"

docker-compose-services/postgres/docker-compose.postgres.yaml

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+version: '3.6'
+services:
+  postgres:
+    container_name: ddev-${DDEV_SITENAME}-postgres
+    image: mdillon/postgis:11
+    ports:
+      - 32784:5432
+    environment:
+      - POSTGRES_PASSWORD=db
+      - POSTGRES_USER=db
+      - POSTGRES_DB=db
+    volumes:
+      - ".:/mnt/ddev_config"
+    labels:
+      com.ddev.site-name: ${DDEV_SITENAME}
+      com.ddev.approot: $DDEV_APPROOT
+  web:
+    links:
+      - postgres:postgres