Update README, streamline demo

[fernando-mc]

Hello @ShubhamTatvamasi,

I made a few updates that I think might make this demo a little easier to get started with.

A few notes on my setup:

• I'm using a local AGW within a Vagrant VM
• I had already setup the AGW/Orc8r/NMS

I modified the Vagrantfile like we discussed and included some of the steps used to make ansible automatically trusted by the srsRAN Vagrant VM.

Following these instructions I am able to see traffic flowing from the srsRAN UE and showing up within the NMS for the tested subscriber.

Let me know if you have any questions! Happy to make any changes that would be useful.

[ShubhamTatvamasi]

Thanks for these updates @fernando-mc. This will help everyone to understand things better.