Added Tenable VMS

Added app, documentation and image

Author: shalin24999

docs/Tenable_vulnerability_management.md

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+## Tenable Vulnerability Management
+- An app to interact with tenable cloud from Shuffle.
+- This app will help to manage assets, schedule scans, push policies, view scan findings, and control multiple Nessus scanners from the cloud.
+
+![App_image](https://github.com/shalin24999/security-openapis/blob/master/tenable/Tenable_Vulnerability_app.png?raw=true)
+
+## Authentication
+- Tenable.io generates a unique set of API keys for each user account. We need  X-ApiKeys for authentication.
+    #### To generate API keys for your own account :
+    - Login into https://cloud.tenable.com/#/ 
+    - Go to https://cloud.tenable.com/tio/app.html#/settings/my-account/api-keys 
+    - Click on Generate *(**Caution**: Any existing API keys are replaced when you click the Generate button. You must update the applications where the previous API keys were used.)*
+    - Copy the new access and secret keys to a safe location. *(**Caution**: Be sure to copy the access and secret keys before you close the API Keys tab. After you close this tab, you cannot retrieve the keys.)*
+    
+    #### Authentication in Shuffle:
+    - In Apikey parameter you need to enter the access and secret key in the following **format**:
+        - accessKey=ACCESS_KEY; secretKey=SECRET_KEY;
+        - **Example**:accessKey=d95e12bcd59c6725823f3f84ea588bb46846447f8037b6e211d1c5e21bbbf847; secretKey=ae66a1r7761fb67da8b91bd7f8aea1e9de1cc38f40feb67cd920e93a5913a2ef
+
+## Actions
+Read the official documentation for each actions which is available [here](https://developer.tenable.com/reference#io-v1-access-groups).
+
+