Added a section about updating submodules
Added a section about updating submodules

The process for updating rustfmt is quite involved because of the way everything is configured. This section covers the steps for updating rustfmt and rationale behind them.
graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust