add stix viz doc

extension-definition-specifications/incident-ef7/stix-viz-config.txt

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+{
+    "incident": {
+	"embeddedRelationships": [ [ "extensions.extension-definition—​ef765651-680c-498d-9894-99799f2fa126.events.event_ref", "has_event", true],
+				   [ "extensions.extension-definition—​ef765651-680c-498d-9894-99799f2fa126.tasks.task_ref", "has_task", true]
+				 ]
+    },
+    "event": {
+	"embeddedRelationships": [[ "sightings_refs", "evidence", true]]
+    }
+}

extension-definition-specifications/using-stxviz.md

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+## STIX Viz
+
+### Setup
+
+- Clone https://github.com/oasis-open/cti-stix-visualization
+- Add the icon files in the icons directory of any extension you are using to stix2viz/stix2viz/icons
+
+### Use STIXViz
+
+- Click on index.html to bring up a "local" copy of STIXViz in your browser
+- Cut and paste the contents of stix-viz-config.json of any extension you are using info the --Configuration-- text box at the bottom of the web page
+- Choose a STIX file
+
+### Tips
+
+- You can remove a type of STIX object from the graph by clicking on its name in the "Legend"
+- Clicking on the node in the graph will show you the STIX JSON on the right.