Warn in installation/Getting Started guides about common problems and how to resolve them

[StevenMaude]

Things don't always work according to plan, e.g. GitHub Actions can fail, Gitpod might be down, people may miss steps out.

Some kind of common errors and problem resolution might be helpful for these two reasons:

• it makes readers realise that things can be tricky (comment from user feedback)
• it might help readers actually fix the problem, if the "happy path" fails for some reason

Another example: linter warnings in local VSCode installation, because packages aren't installed directly into the host system.