Adding Documentation of Mapper

Adding documentation of Mapper on readthedocs

Change-Id: I80ec21296ec42ef21552a9e93839ca5209a27a58
Issue-ID: DCAEGEN2-936
Signed-off-by: Pooja03 <pm00501616@techmahindra.com>
diff --git a/docs/sections/services/mapper/flow.rst b/docs/sections/services/mapper/flow.rst
new file mode 100644
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+============
+Flow
+============
+.. [#] VNF submits SNMP traps to the SNMP trap collecto.
+.. [#] Collector converts the trap into JSON format and publishes it on DMaaP topic **ONAP-COLLECTOR-SNMPTRAP**
+.. [#] The Universal VES Adapter(UVA) microservice has subscribed to this DMaaP topic.
+.. [#] On receiving an event from DMaaP, the adapter uses the corresponding mapping file from repository and converts received event into the VES event. It uses the enterprise ID from the received event to find the required mapping file. 
+.. [#] Those SNMP Traps for which no mapping file is identified, a default mapping file is used with generic mappings to create the VES object.
+.. [#] The VES formatted Event will be then published on DMaaP topic **unauthenticated.SEC_FAULT_OUTPUT**.
+
+
+.. image:: ./flow.png
+   :height: 100px
+   :width: 200 px
+   :scale: 50 %
+   :alt: alternate text
+   :align: left
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