Fix> Add .env usage file!!!

Readme.md

@@ -54,6 +54,14 @@ or similar token, so the API is open for everybody.
 
 I suppose you have installed docker and docker-compose. If not, try [here](https://docs.docker.com/compose/install/)
 
+Create the `.env` file and add this lines:
+```
+POSTGRES_DB=postgres
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=postgres
+DJANGO_SETTINGS_MODULE=application.settings-pg #Very important
+```
+
 Run:
 ```sh
 $ docker-compose up