[CONTRIBUTING] Improved wording and TOC.

CONTRIBUTING.md

@@ -1,4 +1,16 @@
-# Contributing
+# Contributing  <!-- omit in toc -->
+
+**Table of Contents**
+
+- [How to Contribute](#how-to-contribute)
+- [Pull Requests](#pull-requests)
+- [Leaderboard Submissions](#leaderboard-submissions)
+- [Code Style](#code-style)
+- [Contributor License Agreement ("CLA")](#contributor-license-agreement-cla)
+
+---
+
+## How to Contribute
 
 We want to make contributing to CompilerGym as easy and transparent
 as possible. The most helpful ways to contribute are:
@@ -16,8 +28,10 @@ as possible. The most helpful ways to contribute are:
    * Pull requests. Please see below for details. The easiest way to get stuck
      is to grab an [unassigned "Good first issue"
      ticket](https://github.com/facebookresearch/CompilerGym/issues?q=is%3Aopen+is%3Aissue+no%3Aassignee+label%3A%22Good+first+issue%22)!
-   * Add new features not on the roadmap. Examples could include adding support
-     for new compilers, producing research results using CompilerGym, etc.
+   * Add new features not on [the
+     roadmap](https://facebookresearch.github.io/CompilerGym/about.html#roadmap).
+     Examples could include adding support for new compilers, producing research
+     results using CompilerGym, etc.
 
 
 ## Pull Requests
@@ -32,9 +46,9 @@ We actively welcome your pull requests.
 3. If you've added code that should be tested, add tests.
 4. If you've changed APIs, update the [documentation](/docs/source).
 5. Ensure the `make test` suite passes.
-6. Make sure your code lints (see "Code Style" below).
-7. If you haven't already, complete the Contributor License Agreement
-   ("CLA").
+6. Make sure your code lints (see [Code Style](#code-style) below).
+7. If you haven't already, complete the [Contributor License Agreement
+   ("CLA")](#contributor-license-agreement-cla).
 
 
 ## Leaderboard Submissions
@@ -69,15 +83,17 @@ is simple:
   style](https://google.github.io/styleguide/cppguide.html) with 100
   character line length and `camelCaseFunctionNames()`.
 
-We use [pre-commit](/.pre-commit-config.yaml) to format our code to
-enforce these rules. Before submitting pull requests, please run
-pre-commit to ensure the code is correctly formatted.
+We use [pre-commit](https://pre-commit.com/) to ensure that code is formatted
+prior to committing. Before submitting pull requests, please run pre-commit. See
+the [config file](/.pre-commit-config.yaml) for installation and usage
+instructions.
 
 Other common sense rules we encourage are:
 
 * Prefer descriptive names over short ones.
 * Split complex code into small units.
 * When writing new features, add tests.
+* Make tests deterministic.
 * Prefer easy-to-use code over easy-to-read, and easy-to-read code over
   easy-to-write.