Rollup merge of rust-lang#57505 - rust-lang:nrc-patch-1, r=alexcrichton

Remove submodule step from README

Since the bootstrap does it now

Author: Centril

README.md

@@ -38,7 +38,6 @@ Read ["Installation"] from [The Book].
 3. Build and install:
 
     ```sh
-    $ git submodule update --init --recursive --progress
     $ ./x.py build && sudo ./x.py install
     ```