Documentation/git-svnimport.txt: fix typo.

This was noticed by Frederik Schwarzer.  SVN's repository by default has
trunk, tags/, and branch_es_/.
Signed-off-by: NGerrit Pape <pape@smarden.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Documentation/git-svnimport.txt

@@ -27,7 +27,7 @@ repository, or incrementally import into an existing one.
 SVN access is done by the SVN::Perl module.
 
 git-svnimport assumes that SVN repositories are organized into one
-"trunk" directory where the main development happens, "branch/FOO"
+"trunk" directory where the main development happens, "branches/FOO"
 directories for branches, and "/tags/FOO" directories for tags.
 Other subdirectories are ignored.