Update the README concerning write modes.
Update the README concerning write modes.

Add checkstyle and more detail on each of the write modes.

flutterhash/rustfmt,graydon/rust,aidancully/rust,aidancully/rust,studoot/rustfmt,aidancully/rust,aidancully/rust,Emilgardis/rustfmt,graydon/rust,graydon/rust,graydon/rust,studoot/rustfmt,graydon/rust,rust-lang/rustfmt,aidancully/rust,SingingTree/rustfmt,aidancully/rust,graydon/rust,rust-lang/rustfmt,SingingTree/rustfmt,Emilgardis/rustfmt