Rollup merge of rust-lang#41391 - durka:patch-40, r=petrochenkov

remove disclaimer from bootstrap/README.md

src/bootstrap/README.md

@@ -4,10 +4,6 @@ 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.
 
-> **Note**: This build system is currently under active development and is not
-> intended to be the primarily used one just yet. The makefiles are currently
-> the ones that are still "guaranteed to work" as much as possible at least.
-
 ## Using rustbuild
 
 The rustbuild build system has a primary entry point, a top level `x.py` script: