Add system requirement / suggested spec to setup page

Add "system requirement" / "suggested spec" to setup page: Developer/Setup/DevSetupIndex.md

Something like:

# Setup Environment For Development

## Suggested System / VM Spec
### VM Installation
- OS: Ubuntu 18.04 64bit
- CPU: at least 2 cores (not emulated virtual core)
- Memory: ....
- ....

### Direct Ubuntu Installation 
- ....

## Follow the following instructions to setup environment
- [Setup Script](ENVSetupScript.md)
- [Setup Manually](ManualENVSetup.md)