Merge branch 'km/log-showsignature-doc' into maint

Doc update.

* km/log-showsignature-doc:
  config.txt: add an entry for log.showSignature

Documentation/config.txt

@@ -2151,6 +2151,10 @@ log.showRoot::
 	Tools like linkgit:git-log[1] or linkgit:git-whatchanged[1], which
 	normally hide the root commit will now show it. True by default.
 
+log.showSignature::
+	If true, makes linkgit:git-log[1], linkgit:git-show[1], and
+	linkgit:git-whatchanged[1] assume `--show-signature`.
+
 log.mailmap::
 	If true, makes linkgit:git-log[1], linkgit:git-show[1], and
 	linkgit:git-whatchanged[1] assume `--use-mailmap`.