Make numbered list use only 1.

Addressing PR comment.

Author: smanilov

Diff for: src/about-this-guide.md

@@ -8,25 +8,25 @@ There are several parts to this guide:
 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 Rust][p2]:
+1. [Contributing to Rust][p2]:
    Contains information that should be useful no matter how you are contributing,
    about procedures for contribution, using git and Github, stabilizing features, etc.
-3. [Bootstrapping][p3]:
+1. [Bootstrapping][p3]:
    Describes how the Rust compiler builds itself using previous versions, including
    an introduction to the bootstrap process and debugging methods.
-4. [High-level Compiler Architecture][p4]:
+1. [High-level Compiler Architecture][p4]:
    Discusses the high-level architecture of the compiler and stages of the compile process.
-5. [Source Code Representation][p5]:
+1. [Source Code Representation][p5]:
    Describes the process of taking raw source code from the user
    and transforming it into various forms that the compiler can work with easily.
-6. [Supporting Infrastructure][p6]:
+1. [Supporting Infrastructure][p6]:
    Covers command-line argument conventions, compiler entry points like rustc_driver and
    rustc_interface, and the design and implementation of errors and lints.
-7. [Analysis][p7]:
+1. [Analysis][p7]:
    Discusses the analyses that the compiler uses to check various properties of the code
    and inform later stages of the compile process (e.g., type checking).
-8. [MIR to Binaries][p8]: How linked executable machine code is generated.
-9. [Appendices][p9] at the end with useful reference information.
+1. [MIR to Binaries][p8]: How linked executable machine code is generated.
+1. [Appendices][p9] at the end with useful reference information.
    There are a few of these with different information, including a glossary.
 
 [p1]: ./building/how-to-build-and-run.html