docs(README): Document how to test an in-development version of Basep…

…late in Snoodev (#756)

README.md

@@ -47,3 +47,25 @@ actions on push.
 Specific hooks can be [temporarily disabled](https://pre-commit.com/#temporarily-disabling-hooks).
 
 You can install hooks only for a specific step (i.e. [pre-push](https://pre-commit.com/#pre-commit-during-push)).
+
+## Testing in Snoodev
+
+You can upgrade any service to use in development Baseplate code in Snoodev by
+editing the requirements file for the service you would like to use for testing.
+Update the the Baseplate requirement to pull from Github instead, like this:
+
+```
+diff --git a/requirements.txt b/requirements.txt
+index aef8ad8..d32a078 100644
+--- a/requirements.txt
++++ b/requirements.txt
+-baseplate==2.5.7
++git+https://github.com/reddit/baseplate.py@<ref>#egg=baseplate
+```
+
+In this case the ref can be either a commit hash or a branch name. After making
+this update you can check if the service works in Snoodev.
+
+> **Warning**
+> Never deploy this change to production. Production should always use a Baseplate
+> semantic version that has been tagged, and released.