Canonicalize part 1 name (#788)

Author: kraai

src/about-this-guide.md

@@ -6,7 +6,7 @@ development.
 
 There are six parts to this guide:
 
-1. [Building and Debugging to `rustc`][p1]: Contains information that should be
+1. [Building and debugging `rustc`][p1]: Contains information that should be
    useful no matter how you are contributing, about building, debugging,
    profiling, etc.
 2. [Contributing to `rustc`][p1-5]: Contains information that should be useful