update installation steps for ScanCode, standardized codeblock spacing

[altsalt]

While installing grimoirelab-graal I found that ScanCode now has current releases. Additionally, I'm installing everything in my home directory (aside from go and the apt-get calls) and updated the instructions to reflect how to achieve this. Also, I cleaned up and standardized the way that code blocks are displayed.

I have not yet checked whether something needs to be updated on a ReadTheDocs site.