Expand dev docs for E2E tests running against EE version (#25114)

Co-authored-by: Jeff Bruemmer <jeff.bruemmer@gmail.com>

docs/developers-guide/e2e-tests.md

@@ -92,3 +92,21 @@ Cypress records videos of each test run, which can be helpful in debugging. Addi
 
 These files can be found under the “Artifacts” tab in Circle:
 ![Circle CI Artifacts tab](https://user-images.githubusercontent.com/691495/72190614-f5995380-33cd-11ea-875e-4203d6dcf1c1.png)
+
+## Running Cypress tests against EE version of Metabase
+
+Prior to running Cypress, make sure you have a valid enterprise token. We have a special `describe` block called `describeEE` that will conditionally skip or run tests based on the existence of two environment variables:
+
+- `MB_EDITION`
+- `MB_PREMIUM_EMBEDDING_TOKEN`
+
+```
+MB_EDITION=ee MB_PREMIUM_EMBEDDING_TOKEN=xxxxxx yarn test-cypress-open
+```
+
+If you navigate to the `/admin/settings/license` page, the license input field should be disabled and already populated. It should say: "Using MB_PREMIUM_EMBEDDING_TOKEN".
+
+
+- If tests under `describeEE` block are greyed out and not running, make sure you entered the environment variables correctly.
+- If tests start running but the enterprise features are missing: make sure that the token is still valid. 
+- If everything with the token seems to be okay, go nuclear and destroy all Java processes: run `killall java` and restart Cypress.