include ./ in example x.py commands for smoother copy-paste experience

The current directory is typically not on the user's $PATH.

Author: zackmdavis

src/rustdoc.md

@@ -33,13 +33,13 @@ does is call the `main()` that's in this crate's `lib.rs`, though.)
 
 ## Cheat sheet
 
-* Use `x.py build --stage 1 src/libstd src/tools/rustdoc` to make a useable
+* Use `./x.py build --stage 1 src/libstd src/tools/rustdoc` to make a useable
   rustdoc you can run on other projects.
   * Add `src/libtest` to be able to use `rustdoc --test`.
   * If you've used `rustup toolchain link local /path/to/build/$TARGET/stage1`
     previously, then after the previous build command, `cargo +local doc` will
     Just Work.
-* Use `x.py doc --stage 1 src/libstd` to use this rustdoc to generate the
+* Use `./x.py doc --stage 1 src/libstd` to use this rustdoc to generate the
   standard library docs.
   * The completed docs will be available in `build/$TARGET/doc/std`, though the
     bundle is meant to be used as though you would copy out the `doc` folder to