readability

Author: tshepang

src/doc/rustc-dev-guide/src/building/bootstrapping/writing-tools-in-bootstrap.md

@@ -7,7 +7,7 @@ There are three types of tools you can write in bootstrap:
   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 "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.
+  including target libraries, and it only works for stage 0.
 
 - **`Mode::ToolStd`**