Reword confusing sentence

Author: jyn514

src/building/bootstrapping.md

@@ -157,9 +157,9 @@ The convention `x.py` uses is that:
 
 ### Building vs. Running
 
-Note that this implies the stage N compiler is _not_ the same as the compiler
-built by `build --stage N compiler/rustc` -- that's 'stage N artifacts'
-('the compiler built by stage N').
+
+Note that `build --stage N compiler/rustc` **does not** build the stage N compiler:
+instead it builds the stage _N+1_ compiler _using_ the stage N compiler.
 
 In short, _stage 0 uses the stage0 compiler to create stage0 artifacts which
 will later be uplifted to be the stage1 compiler_.