Add backticks to code

Co-authored-by: Camelid <37223377+camelid@users.noreply.github.com>

Author: jyn514

src/building/bootstrapping.md

@@ -143,7 +143,7 @@ another program we are building with the stage N compiler:
 `build --stage N compiler/rustc` is linking the stage (N+1) compiler to the `std`
 built by the stage N compiler.
 
-Here is a chart of a full build using x.py:
+Here is a chart of a full build using `x.py`:
 
 <img alt="A diagram of the rustc compilation phases" src="../img/rustc_stages.svg" class="center" />
 
@@ -187,7 +187,7 @@ to the `std` that `stage2/rustc` would compile.
 However, when cross-compiling, stage1 `std` will only run on the host.
 So the stage2 compiler has to recompile `std` for the target.
 
-### Why does only libstd use cfg(bootstrap)?
+### Why does only libstd use `cfg(bootstrap)`?
 
 The `rustc` generated by the stage0 compiler is linked to the freshly-built
 `std`, which means that for the most part only `std` needs to be cfg-gated,