Add section about making changes

docs/development_guide.md

@@ -103,4 +103,19 @@ and have built the typescript. To ensure that it's all working, you can run
 
 You can follow the instructions in the [README](../README.md) to generate and update the registration file, as well as creating a testing Slack app and workspace. You should enable RTM support in the config, as Slack will not be able to push events to your local bridge.
 
-Make sure that you copy the generated registration file to `~/slack-bridge-env/synapse` and add an entry for it in the `homeserver.yaml` before starting the synapse container.
+Make sure that you copy the generated registration file to `~/slack-bridge-env/synapse` and add an entry for it in the `homeserver.yaml` before starting the synapse container.
+
+## Making changes
+
+Whenever you want to make changes to the codebase, you must:
+
+```bash
+git fetch matrix-org
+git checkout matrix-org/develop
+git checkout -b yourfeaturname
+npm i
+```
+
+You should always work within the `src` directory. It is helpful to have a code editor setup with linting enabled so you can see mistakes as you work. Always remember to run `npm run build` before commiting or testing so that you know the latest changes work.  
+
+Before commiting your work, ensure that the tests pass locally with `npm test`. If you are making changes to packages, ensure that `package-lock.json` is included in the commit.