Merge branch 'kf/gpg-sig-verification-doc'

Documentation for "git merge --verify-signatures" has been updated
to clarify that the signature of only the commit at the tip is
verified.  Also the phrasing used for signature and key validity is
adjusted to align with that used by OpenPGP.

* kf/gpg-sig-verification-doc:
Documentation: clarify signature verification

diff --combined Documentation/merge-options.txt
index dfb43d000fa8f539a99bae771fca87abfd46e507,30808a01e7657164618c18182704768e2df0d37e..5b4a62e93624bc8289c835631aab5d5f13dff708
--- 1/Documentation/merge-options.txt
--- 2/Documentation/merge-options.txt
+++ b/Documentation/merge-options.txt
@@@ -89,8 -89,11 +89,11 @@@ option can be used to override --squash
  
  --verify-signatures::
  --no-verify-signatures::
-       Verify that the commits being merged have good and trusted GPG signatures
-       and abort the merge in case they do not.
+       Verify that the tip commit of the side branch being merged is
+       signed with a valid key, i.e. a key that has a valid uid: in the
+       default trust model, this means the signing key has been signed by
+       a trusted key.  If the tip commit of the side branch is not signed
+       with a valid key, the merge is aborted.
  
  --summary::
  --no-summary::
@@@ -114,11 -117,3 +117,11 @@@ ifndef::git-pull[
        reporting.
  
  endif::git-pull[]
 +
 +--allow-unrelated-histories::
 +      By default, `git merge` command refuses to merge histories
 +      that do not share a common ancestor.  This option can be
 +      used to override this safety when merging histories of two
 +      projects that started their lives independently. As that is
 +      a very rare occasion, no configuration variable to enable
 +      this by default exists and will not be added.