Add SwiftShell
Add SwiftShell

## Project URL
https://github.com/kareman/SwiftShell

## Category
Command Line

## Description
A Swift framework for shell scripting and running shell commands.

## Why it should be included to `awesome-ios` (mandatory)
There aren't any other frameworks for running shell commands in the list. Most of the others in the "Command Line" category are command line arguments parsers.

## Checklist
* [ x ] Has 50 Github stargazers or more
* [ x ] Only one project/change is in this pull request
* [ x ]  Isn't an archived project
* [ x ] Has more than one contributor
* [ x ]  Has unit tests, integration tests or UI tests
* [ x ] Addition in chronological order (bottom of category)
* [ N/A ] Supports iOS 9 / tvOS 10 or later
* [ x ] Supports Swift 4 or later
* [ x ] Has a commit from less than 2 years ago
* [ x ] Has a **clear** README in English
vsouza/awesome-ios,arasu01/awesome-ios