Update installation guidance for developers

[sarahcollyer]

Is your feature request related to a problem? Please describe.
The developer guidance could be more detailed, especially when it comes to installation on ONS machines.

Describe the solution you'd like
Clearer guidance for installation for developers, similar to the guidance on the Duck Book.

Describe alternatives you've considered
None

Additional context
I struggled to figure out how to properly install the requirements for developers. It might be a me problem, but on the off chance it isn't it may be a good idea to make the guidance clearer. Those with more experience/not using ONS machines may not need this, but can easily ignore if they already know what do.