docs: Clarify that enterpriseBaseURL requires /api/v3 suffix (#292)

Signed-off-by: Andreas Lindhé <[email protected]>

Author: lindhe

docs/services/github.md

@@ -7,7 +7,9 @@ The GitHub notification service changes commit status using [GitHub Apps](https:
 - `appID` - the app id
 - `installationID` - the app installation id
 - `privateKey` - the app private key
-- `enterpriseBaseURL` - optional URL, e.g. https://git.example.com/
+- `enterpriseBaseURL` - optional URL, e.g. https://git.example.com/api/v3
+
+> ⚠️ _NOTE:_ Specifying `/api/v3` in the `enterpriseBaseURL` is required until [argoproj/notifications-engine#205](https://github.com/argoproj/notifications-engine/issues/205) is resolved.
 
 ## Configuration