Feature: Improve documentation

[rileychh]

Description

• The current documentation has many grammar errors and structural issues. This issue aims to fix them.

How to Implement

Goals:

• Lint the documentation with markdownlint. (Lint documentation with markdownlint #193)
• Update the issue template to better suit the project's needs, e.g. Remove the desktop and web section in the bug report template. (Update GitHub templates #201)
• Add a checklist to the PR template so that the contributor can check basic requirements themselves. (Update GitHub templates #201)
• Update Code of Conduct to v2.1 (see their changelog).
• Update the README.md to make it easier to read unrendered, easier to understand, and have fewer grammar errors.
• Update the CONTRIBUTING.md to make it easier for new contributors to get started and follow the CoC and license.

Each goal will have its own PR, and we can discuss them there or in Discord. Please feel free to comment with your opinions on these goals.

Design (optional)

The design of each goal can be discussed in its respective PRs.

Additional Context (optional)

• This issue is a continuation of Improve documentation by rewriting and using linter #190.