Disk space requirement when building should be indicated in the readme

[krk]

Currently, around 54 GB is required for a default incremental build (x.py build -i).

We may include some tips to decrease disk space requirements in the readme, potentially not building all LLVM targets etc.

[Mark-Simulacrum]

I see a 3.6 GB build locally with a fresh checkout and a single run of ./x.py build -i. Could you clarify if that's the same as your configuration?

[krk]

I am building on Windows Subsystem for Linux as Windows build didn't work.

Fresh checkout + single run is correct. I am attaching a dir size report [1], please note that I ran x.py test for a single test since.

[1] https://gist.github.com/krk/90ef18338975b27fc7c79a8439bbed40

[Mark-Simulacrum]

I'm afraid I cannot reproduce and as such am uncertain whether we can effectively document this; I also don't have access to a WSL environment so I can't test there either.

It would also be helpful to have a copy of your config.toml.

[krk]

Here is my config.toml https://gist.github.com/krk/73bd0f11bd1aecbf24617662f1d148e2

Inclusion of some kind of estimate could be helpful to first-time builders, even just giving a ball park. As examples, Chromium and Firefox gives estimated disk space usages.

[Mark-Simulacrum]

So that's a non-standard configuration; I see ~30 GB locally with it.

I think it may be somewhat helpful to add a note that a debug configuration could be upwards of 30 GB, however a default configuration (with no configuration flags changed) you'll see about a 3.6 GB build. If you'd like to make a PR adding that, please go ahead! We should probably add it to the CONTRIBUTING file instead of the README, though.