Add PMSH documentation

*Add base PM Subscription Handler documentation

Issue-ID: DCAEGEN2-1837
Change-Id: I17bb587ef56704e0a122d65c7d29a2998489ce9c
Signed-off-by: dfarrelly <david.farrelly@est.tech>
diff --git a/docs/sections/services/serviceindex.rst b/docs/sections/services/serviceindex.rst
index c046157..e7faca4 100644
--- a/docs/sections/services/serviceindex.rst
+++ b/docs/sections/services/serviceindex.rst
@@ -18,6 +18,7 @@
    ./dfc/index.rst
    ./heartbeat-ms/index.rst
    ./pm-mapper/index.rst
+   ./pm-subscription-handler/index.rst
    ./bbs-event-processor/index.rst
    ./son-handler/index.rst
    ./restconf/index.rst