Document behavior of --timestamp when only FROM is used
Fixes:
@@ -652,6 +652,8 @@ specified and therefore not changed, allowing the image's sha256 hash to remain
same. All files committed to the layers of the image will be created with the
timestamp.
+If the only instruction in a Containerfile is `FROM`, this flag has no effect.
+
#### **--tls-verify**
Require HTTPS and verify certificates when talking to container registries
