Added SPCI to the glossary

Change-Id: I576ae161477f4a69336d15a7741e566bb103124a
Signed-off-by: Artsem Artsemenka <artsem.artsemenka@arm.com>
diff --git a/docs/glossary.rst b/docs/glossary.rst
index afe0acf..45caf46 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -129,6 +129,9 @@
    SP
       Secure Partition
 
+   SPCI
+      Secure Partition Client Interface
+
    SPD
       Secure Payload Dispatcher