Add note about running apps

[sarah-witt]

What does this PR do?

Adds a troubleshooting note in the readme about running apps

Motivation

Additional Notes

In the future, let's log a warning about this in the check.

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have changelog/ and integration/ labels attached