Rollup merge of rust-lang#39527 - king6cong:bootstrap-doc, r=alexcrichton

README path correction

Author: frewsxcv

src/bootstrap/bin/main.rs

@@ -11,8 +11,8 @@
 //! rustbuild, the Rust build system
 //!
 //! This is the entry point for the build system used to compile the `rustc`
-//! compiler. Lots of documentation can be found in the `README.md` file next to
-//! this file, and otherwise documentation can be found throughout the `build`
+//! compiler. Lots of documentation can be found in the `README.md` file in the
+//! parent directory, and otherwise documentation can be found throughout the `build`
 //! directory in each respective module.
 
 #![deny(warnings)]