Add some additional documentation to the README (#1068)

This pull request adds a small amount of additional, helpful information that I feel first-time users like myself might find useful as they try to use this tool

Signed-off-by: Ashish Banerjee <[email protected]>

README.md

@@ -112,17 +112,19 @@ echo "build --config=clang" >> user.bazelrc
 
 #### Install Python libraries
 
+It is advisable to use the same version of Python as the one listed at the top of `tools/base/requirements.txt`. While other versions may also work, the chances of success are greatest if using the same one.
+
 Recommended: Use `virtualenv` to avoid conflicts between Nighthawk's Python package version requirements and other versions already on your system:
 ```
-virtualenv ~/my_nh_venv
+python3 -m venv ~/my_nh_venv
 source ~/my_nh_venv/bin/activate
 ```
 
 Note: Avoid creating the environment under the Nighthawk project directory.
 
 Install Python packages required for Nighthawk (whether using `virtualenv` or not):
 ```
-pip3 install --user -r requirements.txt
+pip3 install --user -r tools/base/requirements.txt
 ```
 
 If `pip3 install` fails, you will need to troubleshoot the Python environment before attempting to build and test Nighthawk.