update the beginning part of bootstrap/README.md

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/README.md

@@ -1,8 +1,7 @@
 # rustbuild - Bootstrapping Rust
 
-This is an in-progress README which is targeted at helping to explain how Rust
-is bootstrapped and in general, some of the technical details of the build
-system.
+This README is aimed at helping to explain how Rust is bootstrapped and in general,
+some of the technical details of the build system.
 
 Note that this README only covers internal information, not how to use the tool.
 Please check [bootstrapping dev guide][bootstrapping-dev-guide] for further information.