README for NBI

when looking at OOM Charts, it's important to know what they're
deploying and what are the requirements. This commit is doing it
for NBI project

Change-Id: I8200bc1a2ce06073af898a38ef4d72511969d03d
Issue-ID: OOM-1453
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>
diff --git a/kubernetes/nbi/README.md b/kubernetes/nbi/README.md
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+# NBI
+
+## Introduction
+
+NBI stands for NorthBound Interface. It brings to ONAP a set of API that can be
+used by external systems as BSS for example. These API are based on TMF API.
+
+Full description is on [ONAP Read the Doc](https://onap.readthedocs.io/en/latest/submodules/externalapi/nbi.git/docs/offeredapis/index.html).
+
+## Requirements
+
+NBI needs the following ONAP projects to work:
+
+- AAI
+- SO
+- SDC
+- MSB