Change formatting of API documentation

Changed the headings and added a heading level for the definition and
example of use of a function.

Change-Id: Ifab8b13aabb21cd1692a3e700969d8d926b4ccfb
Issue-ID: NONRTRIC-158
Signed-off-by: elinuxhenrik <henrik.b.andersson@est.tech>
diff --git a/docs/sdnc-a1-controller-api.rst b/docs/sdnc-a1-controller-api.rst
index fb6f177..24f9d45 100644
--- a/docs/sdnc-a1-controller-api.rst
+++ b/docs/sdnc-a1-controller-api.rst
@@ -10,9 +10,9 @@
 .. |nbh| unicode:: 0x2011
    :trim:
 
-##################
-SDNC A1 Controller
-##################
+######################
+SDNC A1 Controller API
+######################
 
 The A1 of a Near |nbh| RT |nbsp| RIC can be used through the SDNC A1 Controller.