cxl: Document external user of existing API

Now that libcxl is public, let's document it.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/Documentation/powerpc/cxl.txt b/Documentation/powerpc/cxl.txt
index 2c71ecc..2a230d01 100644
--- a/Documentation/powerpc/cxl.txt
+++ b/Documentation/powerpc/cxl.txt
@@ -133,6 +133,9 @@
     The following file operations are supported on both slave and
     master devices.
 
+    A userspace library libcxl is avaliable here:
+	https://github.com/ibm-capi/libcxl
+    This provides a C interface to this kernel API.
 
 open
 ----
@@ -366,6 +369,7 @@
     enumeration and tuning of the accelerators. Its layout is
     described in Documentation/ABI/testing/sysfs-class-cxl
 
+
 Udev rules
 ==========