feat(compose): add new lecture on running commands in a container

Author: jslvtr

docs/docs/04_docker_intro/05_run_commands_in_docker_containers/README.md

@@ -0,0 +1,24 @@
+# How to run commands inside a Docker container
+
+If you run your API using Docker Compose, with the `docker compose up` command, you may also want to be able to execute arbitrary shell commands in the container.
+
+For example, later on in the course we will look at database migrations.
+
+To execute a database migration, we need to run a specific command, `flask db mgirate`.
+
+If we use Docker Compose, we'll need to run the command inside the running container, and not in a local terminal.
+
+You can run any arbitrary command in a running container like so:
+
+```bash
+docker compose exec web flask db migrate
+```
+
+This command is split into 4 parts:
+
+- `docker compose`: uses the Docker Compose part of the Docker executable
+- `exec`: used to run a command in a specific Docker Compose service
+- `web`: which Docker Compose service to run the command in
+- `flask db migrate`: the command you want to run
+
+That's all! Just remember while following the course, that if I run any commands in my local terminal and you are using Docker Compose, you should precede the commands with `docker compose exec web`.

docs/docs/11_deploy_to_render/06_run_everything_docker_compose/README.md

@@ -31,7 +31,7 @@ volumes:
 The `postgres` image accepts various environment variables, among them:
 
 - `POSTGRES_PASSWORD`, defaulting to `postgres`
-- `POSTGERS_DB`, defaulting to `postgres`
+- `POSTGRES_DB`, defaulting to `postgres`
 - `POSTGRES_USER`, defaulting to `postgres`
 - `POSTGRES_HOST`, defaulting to `localhost`
 - `POSTGRES_PORT`, defaulting to `5432`