Merge branch 'jc/doc-format-patch-clarify-auto-base'

Rephrase the description of "format-patch --base=auto".

* jc/doc-format-patch-clarify-auto-base:
  format-patch (doc): clarify --base=auto

Author: gitster

Documentation/git-format-patch.txt

@@ -689,10 +689,10 @@ You can also use `git format-patch --base=P -3 C` to generate patches
 for A, B and C, and the identifiers for P, X, Y, Z are appended at the
 end of the first message.
 
-If set `--base=auto` in cmdline, it will track base commit automatically,
-the base commit will be the merge base of tip commit of the remote-tracking
+If set `--base=auto` in cmdline, it will automatically compute
+the base commit as the merge base of tip commit of the remote-tracking
 branch and revision-range specified in cmdline.
-For a local branch, you need to track a remote branch by `git branch
+For a local branch, you need to make it to track a remote branch by `git branch
 --set-upstream-to` before using this option.
 
 EXAMPLES