Correct example tag_with_sha

Signed-off-by: Nick Adcock <[email protected]>

Author: zappy-shu

README.md

@@ -131,7 +131,7 @@ Then the image will be tagged with:
 myregistry/myorg/myimage:foo
 myregistry/myorg/myimage:bar
 myregistry/myorg/myimage:lastest
-myregistry/myorg/myimage:c6df8c6
+myregistry/myorg/myimage:sha-c6df8c6
 ```
 
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