Swap space troubleshooting not readily available

[Fang-]

If the urbit process fails to map 2GB of memory during startup, it will helpfully tell you:

see urbit.org/using/install/#about-swap-space for adding swap space

...Except that link just redirects to the /getting-started page, which has no information at all about swap space.

The binary could be updated to give a different url, but probably better to try solving this docs-side first.

[matildepark]

See also urbit/urbit#3627

We don't document swap space anywhere. Should we? @sigilante @gordoncc

Even if we do add this copy, the link is going to change.

[gordoncc]

I feel like @tinnus-napbus knows or could write the docs for this.