CI/DOC: more detailed documentation on how CI works

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

ci-scripts/doc/vm_based_simulator_destroy.md

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+<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="../../doc/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">OAI CI Virtual-Machine-based: Properly Destroy all VM instances</font></b>
+    </td>
+  </tr>
+</table>
+
+## Table of Contents ##
+
+1.  [Introduction](#1-introduction)
+2.  [Detailed Description](#2-detailed-description)
+3.  [Typical Usage](#3-typical-usage)
+
+# 1. Introduction #
+
+```bash
+$ cd /tmp/CI-raphael
+$ ./ci-scripts/oai-ci-vm-tool destroy --help
+OAI CI VM script
+   Original Author: Raphael Defosseux
+   Requirements:
+     -- uvtool uvtool-libvirt apt-cacher
+
+Usage:
+------
+    oai-ci-vm-tool destroy [OPTIONS]
+
+Mandatory Options:
+--------
+    --job-name #### OR -jn ####
+    Specify the name of the Jenkins job.
+
+    --build-id #### OR -id ####
+    Specify the build ID of the Jenkins job.
+
+Options:
+--------
+    --help OR -h
+    Print this help message.
+```
+
+# 2. Detailed Description #
+
+Source file concerned: `ci-scripts/destroyAllRunningVM.sh`
+
+## 2.1. destroy_vm function ##
+
+This is the function that is being called from the main oai-vm-tool script.
+
+The main purpose is to destroy all VM instances whose name matches a pattern.
+
+It also cleans up the `.ssh/known_hosts` file.
+
+# 3. Typical Usage #
+
+```bash
+$ cd /tmp/CI-raphael
+$ ./ci-scripts/oai-ci-vm-tool destroy --job-name raphael --build-id 1
+```
+
+---
+
+You can go back to the [CI dev main page](./ci_dev_home)
+