Add Check Enforcer timeout message. (#14825)

eng/CHECKENFORCER

@@ -1,2 +1,58 @@
 format: v0.1-alpha
 minimumCheckRuns: 1
+timeout: 5
+message: >
+  This pull request is protected by [Check Enforcer](https://aka.ms/azsdk/check-enforcer).
+
+  # What is Check Enforcer?
+
+  Check Enforcer helps ensure all pull requests are covered by at least one
+  check-run (typically an Azure Pipeline). When all check-runs associated
+  with this pull request pass then Check Enforcer itself will pass.
+
+  # Why am I getting this message?
+
+  You are getting this message because Check Enforcer did not detect any
+  check-runs being associated with this pull request within five minutes. This
+  may indicate that your pull request is not covered by any pipelines and so
+  Check Enforcer is correctly blocking the pull request being merged.
+
+  # What should I do now?
+
+  If the **check-enforcer** check-run is not passing and all other check-runs
+  associated with this PR are passing (excluding _license-cla_) then you could
+  try telling _Check Enforcer_ to evaluate your pull request again. You can
+  do this by adding a comment to this pull request as follows:
+
+  ```
+  /check-enforcer evaluate
+  ```
+
+  Typically evaulation only takes a few seconds. If you know that your pull
+  request is not covered by a pipeline and this is expected you can override
+  Check Enforcer using the following command:
+
+  ```
+  /check-enforcer override
+  ```
+
+  Note that using the override command triggers alerts so that follow-up
+  investigations can occur (PRs still need to be approved as normal).
+
+  # What if I am onboarding a new service?
+
+  Often, new services do not have validation pipelines associated with them,
+  in order to bootstrap pipelines for a new service, you can issue the following
+  command as a pull request comment:
+
+  ```
+  /azp run prepare-pipelines
+  ```
+
+  This will run a pipeline that analyzes the source tree and creates the
+  pipelines necessary to build and validate your pull request. Once the pipeline
+  has been created you can trigger the pipeline using the following comment:
+
+  ```
+  /azp run python - [service] - ci
+  ```