Define platform in docker-compose file and update readme (#3808)

Define platform in docker-compose file and remove eliminated step from readme

docs/developer/README.md

@@ -21,16 +21,10 @@ Visit the running application at [http://localhost:8080](http://localhost:8080).
 
 ### Troubleshooting 
 
+#### Line endings and manage.py
 * If you are using Windows, you may need to change your [line endings](https://docs.github.com/en/get-started/getting-started-with-git/configuring-git-to-handle-line-endings). If not, you may not be able to run manage.py. 
 * Unix based operating systems (like macOS or Linux) handle line separators [differently than Windows does](https://superuser.com/questions/374028/how-are-n-and-r-handled-differently-on-linux-and-windows). This can break bash scripts in particular. In the case of manage.py, it uses *#!/usr/bin/env python* to access the Python executable. Since the script is still thinking in terms of unix line seperators, it may look for the executable *python\r* rather than *python* (since Windows cannot read the carriage return on its own) - thus leading to the error `usr/bin/env: 'python\r' no such file or directory` 
 * If you'd rather not change this globally, add a `.gitattributes` file in the project root with `* text eol=lf` as the text content, and [refresh the repo](https://docs.github.com/en/get-started/getting-started-with-git/configuring-git-to-handle-line-endings#refreshing-a-repository-after-changing-line-endings)
-* If you are using a Mac with a M1 chip, and see this error `The chromium binary is not available for arm64.` or an error involving `puppeteer`, try adding this line below into your `.bashrc` or `.zshrc`. 
-
-```
-export DOCKER_DEFAULT_PLATFORM=linux/amd64
-```
-
-When completed, don't forget to rerun `docker-compose up`! 
 
 ## Branch Conventions
 

src/docker-compose.yml

@@ -1,5 +1,6 @@
 services:
   app:
+    platform: linux/amd64
     build: .
     depends_on:
       - db
@@ -74,6 +75,7 @@ services:
       python manage.py runserver 0.0.0.0:8080"
 
   db:
+    platform: linux/amd64
     image: postgres:latest
     environment:
       - POSTGRES_DB=app
@@ -83,6 +85,7 @@ services:
       - "5432:5432"
 
   node:
+    platform: linux/amd64
     build:
       context: .
       dockerfile: node.Dockerfile
@@ -96,6 +99,7 @@ services:
     command: ./run_node_watch.sh
 
   pa11y:
+    platform: linux/amd64
     build:
       context: .
       dockerfile: node.Dockerfile