doc/fix: add instructions for ngsdn-tutorial mininet

Added instructions on how to download and run the ngsdn-tutorial mininet that includes bmv2stratum switch, used in the p4 tutorial.

src/tests/netx22-p4/README.md

@@ -20,23 +20,47 @@ environment as described in
 Remember to source the scenario settings appropriately, e.g., `cd ~/tfs-ctrl && source my_deploy.sh` in each terminal
 you open.
 
-Additionally mininet should be installed, we suggest using the mininet packaged in the [Next-Gen SDN Tutorial][https://github.com/opennetworkinglab/ngsdn-tutorial], as it provides an easy way to deploy mininet dockerized and comes with the BMv2Stratum software switch. 
+Additionally mininet with a p4 switch (bmv2 for example) should be installed, we suggest using the mininet packaged in the [Next-Gen SDN Tutorial][https://github.com/opennetworkinglab/ngsdn-tutorial], as it provides an easy way to deploy mininet dockerized and comes with the BMv2Stratum software switch. 
 
-## Test Execution
+### Next-Gen SDN Tutorial installation
 
-### Mininet 
-To execute this functional test, first make sure that mininet is running the correct topology.
-If you have used the Next-Gen SDN Tutorial for it, you may add the topology provided in the mininet folder of the ngsdn tutorial and add the following make rule to its Makefile
+To install the recommended mininet from the Next-Gen SDN Tutorial follow these steps:
+
+First of all you should have the following dependencies installed:
+
+- Docker v1.13.0+ (with docker-compose)
+- make
+- Python 3
+
+Then clone the repo
+```
+cd ~
+git clone -b advanced https://github.com/opennetworkinglab/ngsdn-tutorial
+```
+
+After the repo is downloaded do the following to download the required docker images
+```
+cd ~/ngsdn-tutorial
+make deps
+```
+
+Add the following make rule to the ~/ngsdn-tutorial/Makefile
 ```
 start-simple: NGSDN_TOPO_PY := topo-simple.py
 start-simple: _start
 ```
 
-After that run
+And copy the topology file from ~/tfs-ctrl/src/tests/netx22-p4/mininet/topo-simple.py to the ~/ngsdn-tutorial/mininet/ directory.
+
+## Test Execution
+
+### Mininet 
+To execute this functional test, first start mininet:
 ```
 make start-simple
 make mn-cli
 ```
+
 You will be prompted with the mininet cli. Run the following and let it run until the end of the experiment
 ```
 client ping server