DOC/MINOR: fix OpenBSD versions where haproxy works

(cherry picked from commit 17d228be14762b282e5262262c45ecee4c265552)
diff --git a/README b/README
index add7f06..e267730 100644
--- a/README
+++ b/README
@@ -39,7 +39,7 @@
   - solaris     for Solaris 8 or 10 (others untested)
   - freebsd     for FreeBSD 5 to 10 (others untested)
   - osx         for Mac OS/X
-  - openbsd     for OpenBSD 3.1 to 5.2 (others untested)
+  - openbsd     for OpenBSD 3.1 and above
   - aix51       for AIX 5.1
   - aix52       for AIX 5.2
   - cygwin      for Cygwin