be more precise about OpenBSD/NetBSD support

xattrs/ACLs need platform specific code and new have none (yet) for them.

README.rst

@@ -65,8 +65,9 @@ Main features
 
 **Platforms Borg works on**
   * Linux
-  * FreeBSD, OpenBSD, NetBSD
   * Mac OS X
+  * FreeBSD
+  * OpenBSD and NetBSD (for both: no xattrs/ACLs support yet)
   * Cygwin (unsupported)
 
 **Free and Open Source Software**

docs/faq.rst

@@ -6,6 +6,7 @@ Frequently asked questions
 
 Which platforms are supported?
     Currently Linux, FreeBSD and MacOS X are supported.
+    OpenBSD and NetBSD work also, except for xattrs and ACLs.
 
     You can try your luck on other POSIX-like systems, like Cygwin,
     other BSDs, etc. but they are not officially supported.