docs: submitting-patches: clarify difference between Acked-by and Reviewed-by

Newcomers to the kernel need to learn the different tags that are
used in commit messages and when to apply them. Acked-by is sometimes
misunderstood, since the documentation did not really clarify (up to
the previous commit) when it should be used, especially compared to
Reviewed-by.

The previous commit already clarified who the usual providers of Acked-by
tags are, with examples. Thus provide a clarification paragraph for
the comparison with Reviewed-by, and give a couple examples reusing the
cases given above, in the previous commit.

Acked-by: Shuah Khan <[email protected]>
Acked-by: Dan Williams <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Acked-by: Krzysztof Kozlowski <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: ojeda

Documentation/process/submitting-patches.rst

@@ -480,6 +480,12 @@ mergers will sometimes manually convert an acker's "yep, looks good to me"
 into an Acked-by: (but note that it is usually better to ask for an
 explicit ack).
 
+Acked-by: is also less formal than Reviewed-by:.  For instance, maintainers may
+use it to signify that they are OK with a patch landing, but they may not have
+reviewed it as thoroughly as if a Reviewed-by: was provided.  Similarly, a key
+user may not have carried out a technical review of the patch, yet they may be
+satisfied with the general approach, the feature or the user-facing interface.
+
 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
 For example, if a patch affects multiple subsystems and has an Acked-by: from
 one subsystem maintainer then this usually indicates acknowledgement of just