Merge branch 'pb/doc-external-diff-env'

Doc update.

* pb/doc-external-diff-env:
  git.txt: correct stale 'GIT_EXTERNAL_DIFF' description
diff --git a/Documentation/diff-generate-patch.txt b/Documentation/diff-generate-patch.txt
index e8ed647..b10ff4c 100644
--- a/Documentation/diff-generate-patch.txt
+++ b/Documentation/diff-generate-patch.txt
@@ -10,7 +10,8 @@
 linkgit:git-diff-files[1]
 with the `-p` option produces patch text.
 You can customize the creation of patch text via the
-`GIT_EXTERNAL_DIFF` and the `GIT_DIFF_OPTS` environment variables.
+`GIT_EXTERNAL_DIFF` and the `GIT_DIFF_OPTS` environment variables
+(see linkgit:git[1]).
 
 What the -p option produces is slightly different from the traditional
 diff format:
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 0bb1cfb..2f72b10 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -551,8 +551,9 @@
 
 `GIT_EXTERNAL_DIFF`::
 	When the environment variable `GIT_EXTERNAL_DIFF` is set, the
-	program named by it is called, instead of the diff invocation
-	described above.  For a path that is added, removed, or modified,
+	program named by it is called to generate diffs, and Git
+	does not use its builtin diff machinery.
+	For a path that is added, removed, or modified,
 	`GIT_EXTERNAL_DIFF` is called with 7 parameters:
 
 	path old-file old-hex old-mode new-file new-hex new-mode