chore: clarify webhook verification

Author: aheckmann

docs/webhooks/overview.mdx

@@ -159,10 +159,9 @@ identify and verify the request. The most important headers are:
 
 To verify the authenticity of the webhook payloads, you can use the `X-Plane-Signature` header.
 This header contains an HMAC SHA-256 signature of the payload, generated using the secret key
-you received when creating the webhook. If the signature matches the expected signature, you can be confident that the payload
-was sent by Plane and has not been tampered with.
-
-Here's how to verify the payload signature in Python:
+you received when creating the webhook. If the signature in the header matches
+the HMAC SHA-256 hash of the incoming payload and your secret, you can be
+confident that the payload was sent by Plane and has not been tampered with.
 
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