Add custom rules to SwiftLint

[uhooi]

References:

• https://github.com/realm/SwiftLint#defining-custom-rules
• https://realm.github.io/SwiftLint/rule-directory.html
• https://shtnkgm.com/2020/05/10/ldd.html

[uhooi]

The reference is a 404 error, so this Issue is closed. https://shtnkgm.com/2020/05/10/ldd.html