Rollup merge of #43045 - PlasmaPower:patch-1, r=Mark-Simulacrum
Rollup merge of #43045 - PlasmaPower:patch-1, r=Mark-Simulacrum

README: note how to enable debugging for rustc

I got stuck on this for a bit, looking for a debug option in `./x.py build --help`.

Diff without newline changes:

Before:

> Various other options are also supported, and are documented in the config file.

After:

> Various other options, such as enabling debug information, are also supported, and are documented in the config file.

aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust