Rollup merge of #61734 - mati865:books, r=alexcrichton

Migrate rust-by-example to MdBook2

Author: Centril

src/bootstrap/doc.rs

@@ -64,7 +64,7 @@ book!(
     EmbeddedBook, "src/doc/embedded-book", "embedded-book", RustbookVersion::MdBook2;
     Nomicon, "src/doc/nomicon", "nomicon", RustbookVersion::MdBook2;
     Reference, "src/doc/reference", "reference", RustbookVersion::MdBook1;
-    RustByExample, "src/doc/rust-by-example", "rust-by-example", RustbookVersion::MdBook1;
+    RustByExample, "src/doc/rust-by-example", "rust-by-example", RustbookVersion::MdBook2;
     RustcBook, "src/doc/rustc", "rustc", RustbookVersion::MdBook1;
     RustdocBook, "src/doc/rustdoc", "rustdoc", RustbookVersion::MdBook2;
 );