Auto merge of rust-lang#17435 - Lunaphied:fix/manual-generation, r=Veykril

docs: fix manual generation instructions

To generate all the requisite files, you need to run `cargo xtask codegen` not `cargo test -p xtask`.

Author: bors

src/tools/rust-analyzer/docs/user/manual.adoc

@@ -21,7 +21,7 @@ The LSP allows various code editors, like VS Code, Emacs or Vim, to implement se
 To improve this document, send a pull request: +
 https://github.com/rust-lang/rust-analyzer/blob/master/docs/user/manual.adoc[https://github.com/rust-analyzer/.../manual.adoc]
 
-The manual is written in https://asciidoc.org[AsciiDoc] and includes some extra files which are generated from the source code. Run `cargo test` and `cargo test -p xtask` to create these and then `asciidoctor manual.adoc` to create an HTML copy.
+The manual is written in https://asciidoc.org[AsciiDoc] and includes some extra files which are generated from the source code. Run `cargo test` and `cargo xtask codegen` to create these and then `asciidoctor manual.adoc` to create an HTML copy.
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