doc: Fix "unexpected indentation" warning.

Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>
Change-Id: I521eed6466fdfef18a92f5237912cb402441044a
diff --git a/docs/components/index.rst b/docs/components/index.rst
index ae78b2b..49986ca 100644
--- a/docs/components/index.rst
+++ b/docs/components/index.rst
@@ -17,4 +17,5 @@
    romlib-design
    sdei
    secure-partition-manager-design
+   spci-manifest-binding
    xlat-tables-lib-v2-design