doc/gitattributes: clarify location of config text

The gitattributes documentation has a section on the "diff"
attribute, with subsections for each of the things you might
want to configure in your diff config section (external
diff, hunk headers, etc). The first such subsection
specifically notes that the definition of the diff driver
should go into $GIT_DIR/config, but subsequent sections do
not.

This location is implied if you are reading the
documentation sequentially, but it is not uncommon for a new
user to jump to (or be referred to) a specific section. For
a new user who does not know git well enough to recognize
the config syntax, it is not clear that those directives
don't also go into the gitattributes file.

This patch just mentions the config file in each subsection,
similar to the way it is mentioned in the first.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -297,7 +297,8 @@ for paths.
 
 Then, you would define a "diff.tex.xfuncname" configuration to
 specify a regular expression that matches a line that you would
-want to appear as the hunk header "TEXT", like this:
+want to appear as the hunk header "TEXT". Add a section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
 
 ------------------------
 [diff "tex"]
@@ -345,7 +346,8 @@ split words in a line, by specifying an appropriate regular expression
 in the "diff.*.wordRegex" configuration variable.  For example, in TeX
 a backslash followed by a sequence of letters forms a command, but
 several such commands can be run together without intervening
-whitespace.  To separate them, use a regular expression such as
+whitespace.  To separate them, use a regular expression in your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
 
 ------------------------
 [diff "tex"]
@@ -373,7 +375,8 @@ resulting text on stdout.
 
 For example, to show the diff of the exif information of a
 file instead of the binary information (assuming you have the
-exif tool installed):
+exif tool installed), add the following section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file):
 
 ------------------------
 [diff "jpg"]