[Documentation] Update Installation

[JackKuo-tw]

1. Fill in missing package
2. Update unprecise word

Summary:

This PR is tested on clean Vagrant Box bento/ubuntu-20.04, add some missing packages needed by ONVM

There is one thing interesting, the original installation doc said ONVM needs Python3, but in my test it also needs Python2, so I added it.

Usage:

This PR includes
Resolves issues
Breaking API changes
Internal API changes
Usability improvements	X
Bug fixes
New functionality
New NF/onvm_mgr args
Changes to starting NFs
Dependency updates
Web stats updates

Merging notes:

• Dependencies: None

TODO before merging :

• [x] PR is ready for review

Test Plan:

Review:

Anyone.

[onvm]

In response to PR creation

CI Message

Aborting, need an authorized user to run CI

[kevindweb]

@JackKuo-tw thanks for looking into this. I thought we got rid of our Python 2 dependencies, do you remember, or have screenshots of where it was necessary? I think it would be better to remove those instances if possible, rather than adding the python 2 package.

[JackKuo-tw]

@kevindweb Please refer to the screenshot below, it looks like dpdk-devbind.py needs python (#! /usr/bin/env python3 in the first line) But I can use Python3 to run it correctly, so I think the problem is I need to link pyhton to python3 in my env.

Although, in this transition period (py2 -> py3), I think add a comment to remind the user is the best way.

After I change the doc, I'll notify you again, thanks.

[JackKuo-tw]

@kevindweb done, please have a look.