Don't use "incremental" to refer to `--keep-stage`

`-C incremental` is sound and --keep-stage is not.

src/building/suggested.md

@@ -136,13 +136,13 @@ lets you use `cargo fmt`.
 [the section on vscode]: suggested.md#configuring-rust-analyzer-for-rustc
 [the section on rustup]: how-to-build-and-run.md?highlight=rustup#creating-a-rustup-toolchain
 
-## Incremental builds with `--keep-stage`.
+## Faster builds with `--keep-stage`.
 
 Sometimes just checking
 whether the compiler builds is not enough. A common example is that
 you need to add a `debug!` statement to inspect the value of some
 state or better understand the problem. In that case, you really need
-a full build. By leveraging incremental, though, you can often get
+a full build. By bypassing bootstrap's cache invalidation, you can often get
 these builds to complete very fast (e.g., around 30 seconds). The only
 catch is this requires a bit of fudging and may produce compilers that
 don't work (but that is easily detected and fixed).