docs(README.md): update.

Author: sciborrudnicki

README.md

@@ -38,12 +38,26 @@ npm install @typescript-package/affix --save-peer
 
 ```typescript
 import {
+  // Abstract.
   Affix,
+  // Class.
   Prefix,
   Suffix
 } from '@typescript-package/affix';
 ```
 
+### Affix
+
+A class to manage affixes (prefixes or suffixes) that can be applied to strings.
+
+### Prefix
+
+A class to manage prefixes that can be applied to strings.
+
+### Suffix
+
+A class to manage suffixes that can be applied to strings.
+
 ## Contributing
 
 Your contributions are valued! If you'd like to contribute, please feel free to submit a pull request. Help is always appreciated.