docs: adjust webhooks docs

Author: saitho

README.md

@@ -153,7 +153,7 @@ Then, create your webhook on GitHub as follows:
 1. Go to your Repository Settings
 2. Select the "Webhooks" option in the left navigation menu
 3. Click the button "Add webhook" at the top right
-4. Add set your server URL as "Payload URL" (ending with `/webhook`), e.g. `https://schema.stackhead.io/webhook`
+4. Add set your server URL as "Payload URL" (ending with `/webhook/github`), e.g. `https://schema.stackhead.io/webhook/github`
 5. Select "application/json" as "Content type"
 6. Set your secret from configuration as "Secret"
 7. Choose the option "Let me select individual events." and enable the folowing events: