Describe the library better in the README file

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

1 files changed, 12 insertions, 1 deletions

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.
 
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