[PATCH] Describe the library better in the README file

[Keith Packard]

Signed-off-by: Keith Packard <keithp at keithp.com>
---

Is this better?

 README | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/README b/README
index 66b36f0..db193b7 100644
--- a/README
+++ b/README
@@ -1,4 +1,15 @@
-libxshmfence - Direct Rendering Infrastructure 3 Extension
+libxshmfence - Shared memory 'SyncFence' synchronization primitive
+
+This library offers a CPU-based synchronization primitive compatible
+with the X SyncFence objects that can be shared between processes
+using file descriptor passing.
+
+There are two underlying implementations:
+
+ 1) On Linux, the library uses futexes
+
+ 2) On other systems, the library uses posix mutexes and condition
+    variables.
 
 All questions regarding this software should be directed at the
 Xorg mailing list:
-- 
1.8.4.4