DOC: skeleton for feature list

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

docs/FEATURE_SET.md

+<table style="border-collapse: collapse; border: none;">
+  <tr style="border-collapse: collapse; border: none;">
+    <td style="border-collapse: collapse; border: none;">
+      <a href="http://www.openairinterface.org/">
+         <img src="./images/oai_final_logo.png" alt="" border=3 height=50 width=150>
+         </img>
+      </a>
+    </td>
+    <td style="border-collapse: collapse; border: none; vertical-align: center;">
+      <b><font size = "5">OpenAirInterface AMF Feature Set</font></b>
+    </td>
+  </tr>
+</table>
+
+**Table of Contents**
+
+1. [5GC Service Based Architecture](#1-5gc-service-based-architecture)
+2. [OAI AMF Available Interfaces](#2-oai-smf-available-interfaces)
+3. [OAI AMF Feature List](#3-oai-smf-feature-list)
+
+# 1. 5GC Service Based Architecture #
+
+![5GC SBA](./images/5gc_sba.png)
+
+# 2. OAI AMF Available Interfaces #
+
+**TO BE COMPLETED**
+
+# 3. OAI SMF Feature List #
+
+**TO BE COMPLETED**