Rollup merge of #142672 - Kobzol:bootstrap-tool-clarification, r=jieyouxu

Clarify bootstrap tools description

The existence of `stage0-bootstrap-tools` suggests the possiblity of `stage1/N-bootstrap-tools`, but that's not really a thing. Also it doesn't fit the new bootstrap model, where `stageN` essentially means that it was built with a `stageN-1` compiler (except for std).

r? ``@jieyouxu``

Author: Kobzol

src/building/bootstrapping/writing-tools-in-bootstrap.md

@@ -4,7 +4,7 @@ There are three types of tools you can write in bootstrap:
 
 - **`Mode::ToolBootstrap`**
   Use this for tools that don’t need anything from the in-tree compiler and can run with the stage0 `rustc`.
-  The output is placed in the "stage0-bootstrap-tools" directory. This mode is for general-purpose tools built
+  The output is placed in the "bootstrap-tools" directory. This mode is for general-purpose tools built
   entirely with the stage0 compiler, including target libraries and only works for stage 0.
 
 - **`Mode::ToolStd`**