SPyTest documentation initial version (sonic-net#1565)

Co-authored-by: Rama Sasthri, Kristipati <rama.kristipati@broadcom.com>

Author: ramakristipati

spytest/Doc/arch.jpg

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+**PLEASE REFER TO intro.md FIRST BEFORE THIS DOCUMENT**
+
+* Prerequisites for executing SpyTest
+    * Server/Laptop or VM running Red Hat or Ubuntu with minimum 10GB HDD.
+      We have tested on Red Hat 4.4.7-9 and Ubuntu 16.04.10
+
+* Tools Installation
+    * Create a folder install under the /projects/scid folder
+    * Download following files from [ActiveState](https://www.activestate.com/products/)
+        * ActiveTcl-8.5.19.8519-x86_64-linux-glibc-2.5-403583.tar.gz
+        * ActivePython-2.7.14.2717-linux-x86_64-glibc-2.12-404899.tar.gz
+    * Install them to /projects/scid folder. After installation the folder structure should look like below
+
+            /projects/scid/tools/ActivPython/2.7.14
+            /projects/scid/tools/ActivPython/2.7.14/lib
+            /projects/scid/tools/ActivPython/2.7.14/etc
+            /projects/scid/tools/ActivPython/2.7.14/licenses
+            /projects/scid/tools/ActivPython/2.7.14/include
+            /projects/scid/tools/ActivPython/2.7.14/doc
+            /projects/scid/tools/ActivPython/2.7.14/bin
+            /projects/scid/tools/ActivPython/2.7.14/share
+            /projects/scid/tools/ActivPython/current -> 2.7.14
+
+            /projects/scid/tools/ActivTcl/
+            /projects/scid/tools/ActivTcl/8.5.19
+            /projects/scid/tools/ActivTcl/8.5.19/lib
+            /projects/scid/tools/ActivTcl/8.5.19/8.5.19
+            /projects/scid/tools/ActivTcl/8.5.19/licenses
+            /projects/scid/tools/ActivTcl/8.5.19/MANIFEST_at8.5.txt
+            /projects/scid/tools/ActivTcl/8.5.19/demos
+            /projects/scid/tools/ActivTcl/8.5.19/include
+            /projects/scid/tools/ActivTcl/8.5.19/doc
+            /projects/scid/tools/ActivTcl/8.5.19/bin
+            /projects/scid/tools/ActivTcl/8.5.19/man
+            /projects/scid/tools/ActivTcl/8.5.19/share
+            /projects/scid/tools/ActivTcl/8.5.19/README-8.5-thread.txt
+            /projects/scid/tools/ActivTcl/8.5.19/license-at8.5-thread.terms
+            /projects/scid/tools/ActivTcl/current -> 8.5.19
+    * SPyTest may also work fine with native Linux packages for python2, pip2, tcl and tclx
+      but this is not exercised well. Similarly it may work well in virtual python environment also.
+
+* TGen Installation
+    * SPyTest needs traffic generator client libraries
+        * Please contact Ixia and STC to get the required APIs for these libraries
+    * The exact files used for validating SPyTest are:
+        * [IxNetwork 8.42](http://downloads.ixiacom.com/support/downloads_and_updates/public/ixnetwork/IxNetworkAPI8.42.1250.2Linux64.bin.tgz)
+        * [STC 4.91](https://support.spirent.com/SpirentCSC/SpirentDownloadsAppPage?rid=10492)
+    * Once installed, create symbolic links so that folder structure looks same as given in
+        [SPYTEST-ROOT]/bin/tgen_folders.txt
+    * IxOS TCL libraries need to be installed before installing the IxNetwork libraries
+    * SPyTest needs IxNetwork to installed on an intermediate server/VM
+        * The exact file used for validating SPyTest is:  [IxNetwork 8.42](http://downloads.ixiacom.com/support/downloads_and_updates/public/ixnetwork/IxNetwork8.42EA.exe)
+    * The IxNetwork Server IP address needs to be given in testbed file as "ix_server"
+    * The IxNetwork API Server needs to be launched before launching SPyTest
+    * For Scapy traffic generator refer to [README.testbed.Setup.md](https://github.com/Azure/sonic-mgmt/blob/master/ansible/doc/README.testbed.Setup.md)
+