Add 'subversion' build dependency to README

Fixes #17725.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>

SVN-Revision: 42343

README

@@ -3,8 +3,8 @@ This is the buildsystem for the OpenWrt Linux distribution.
 Please use "make menuconfig" to configure your appreciated
 configuration for the toolchain and firmware.
 
-You need to have installed gcc, binutils, bzip2, flex, python, perl
-make, find, grep, diff, unzip, gawk, getopt, libz-dev and libc headers.
+You need to have installed gcc, binutils, bzip2, flex, python, perl, make,
+find, grep, diff, unzip, gawk, getopt, subversion, libz-dev and libc headers.
 
 Run "./scripts/feeds update -a" to get all the latest package definitions
 defined in feeds.conf / feeds.conf.default respectively