Fix #1737: Specify toolchain part in building and running

src/building/how-to-build-and-run.md

@@ -277,18 +277,20 @@ default).
 Once you have successfully built `rustc`, you will have created a bunch
 of files in your `build` directory. In order to actually run the
 resulting `rustc`, we recommend creating rustup toolchains. The first
-one will run the stage1 compiler (which we built above). The second
-will execute the stage2 compiler (which we did not build, but which
-you will likely need to build at some point; for example, if you want
-to run the entire test suite).
+command listed below runs the stage1 compiler, which was built in the
+steps above, with the name `stage1`. The second command runs the stage2 
+compiler using the stage1 compiler. This will be needed in the future 
+if running the entire test suite, but will not be built in this page. 
+Building stage2 is done with the same `./x build` command as for stage1,
+specifying that the stage is 2 instead.
 
 ```bash
 rustup toolchain link stage1 build/host/stage1
 rustup toolchain link stage2 build/host/stage2
 ```
 
-Now you can run the `rustc` you built with. If you run with `-vV`, you
-should see a version number ending in `-dev`, indicating a build from
+Now you can run the `rustc` you built with via the toolchain. If you run with 
+`-vV`, you should see a version number ending in `-dev`, indicating a build from
 your local environment:
 
 ```bash