add README.md

Author: ram-amoncar

README.md

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+# @full-pack/string-builder
+
+[![npm](https://img.shields.io/npm/v/@full-pack/string-builder.svg)](https://www.npmjs.com/package/@full-pack/string-builder)
+
+[![jest](https://jestjs.io/img/jest-badge.svg)](https://github.com/jestjs/jest) [![Code Style: Prettier](https://img.shields.io/badge/code_style-prettier-ff69b4.svg)](https://github.com/prettier/prettier)
+
+A lightweight and versatile String Utility Package for Node.js & Browser.
+
+<img src="https://user-images.githubusercontent.com/6517308/121813242-859a9700-cc6b-11eb-99c0-49e5bb63005b.jpg">
+
+
+## Installation
+```sh
+npm install @full-pack/string-builder
+```
+
+### require
+
+```js
+const { ... } = require('@full-pack/string-builder');
+```
+
+### import
+
+```js
+import { ... } from '@full-pack/string-builder';
+```
+
+## APIs
+### Class
+* string-builder
+### Data Members
+* capacity: number
+* length: number
+### Methods
+* insert
+* append
+* prepend
+* appendNewLine
+* prependNewLine
+* appendSpace
+* prependSpace
+* appendArray
+* prependArray
+* appendJSON
+* prependJSON
+* appendCodePoint
+* prependCodePoint
+* replaceSubstring
+* setString
+* getString
+* indexOf
+* lastIndexOf
+* setChar
+* substring
+* trim
+* clear
+* reset
+* clone
+* isFull
+* isEmpty
+
+Full documentation [here](https://full-pack.github.io/string-builder)
+
+## Build
+```
+npm run build
+```
+
+## License
+The MIT License. Full License is [here](LICENSE)