doc: provide guidance on user.name format

It's a frequent misconception that the user.name variable controls
authentication in some way, and as a result, beginning users frequently
attempt to change it when they're having authentication troubles.
Document that the convention is that this variable represents some form
of a human's personal name, although that is not required.  In addition,
address concerns about whether Unicode is supported.

Use the term "personal name" as this is likely to draw the intended
contrast, be applicable across cultures which may have different naming
conventions, and be easily understandable to people who do not speak
English as their first language.  Indicate that "some form" is
conventionally used, as people may use a nickname or preferred name
instead of a full legal name.

Point users who may be confused about authentication to an appropriate
configuration option instead.  Provide a shortened form of this
information in the configuration option description.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/user.txt

@@ -13,7 +13,12 @@ committer.email::
 	Also, all of these can be overridden by the `GIT_AUTHOR_NAME`,
 	`GIT_AUTHOR_EMAIL`, `GIT_COMMITTER_NAME`,
 	`GIT_COMMITTER_EMAIL` and `EMAIL` environment variables.
-	See linkgit:git-commit[1] for more information.
++
+Note that the `name` forms of these variables conventionally refer to
+some form of a personal name.  See linkgit:git-commit[1] and the
+environment variables section of linkgit:git[1] for more information on
+these settings and the `credential.username` option if you're looking
+for authentication credentials instead.
 
 user.useConfigOnly::
 	Instruct Git to avoid trying to guess defaults for `user.email`

Documentation/git-commit.txt

@@ -475,6 +475,12 @@ variables, if set:
 
 (nb "<", ">" and "\n"s are stripped)
 
+The author and committer names are by convention some form of a personal name
+(that is, the name by which other humans refer to you), although Git does not
+enforce or require any particular form. Arbitrary Unicode may be used, subject
+to the constraints listed above. This name has no effect on authentication; for
+that, see the `credential.username` variable in linkgit:git-config[1].
+
 In case (some of) these environment variables are not set, the information
 is taken from the configuration items `user.name` and `user.email`, or, if not
 present, the environment variable EMAIL, or, if that is not set,