Add README

Fixes #2

README.md

@@ -1,10 +1,55 @@
 # xcode-simulator-tool
 
-A description of this package.
+[![Swift 5 compatible][swift-badge]][Swift] [![Xcode 10.2 compatible][xcode-badge]][Xcode] 
 
-## TODO
+This is a tool to manage Xcode simulators and their [root certificates][RootCertificate]. 
 
-* Brew formula
-* README
-* Filter for os types
-* `remove` command that removes simulators
+If you have a certificate for your server in PEM format in a file `myhost.crt`, type:
+
+```bash
+$ xcode-simulator-tool install-ca myhost.crt
+```
+
+It will then install the certificate in all your simulators. You can also specify a specific simulator:
+
+```bash
+$ xcode-simulator-tool install-ca myhost.crt --device-name="iPhone 8"
+```
+
+There are also some other subcommands and options available. `--help` is your friend.
+
+## Installation
+
+#### Using Homebrew
+
+[Homebrew] is the de-facto standard package manager for macOS open-source tools and other things.
+
+```bash
+$ brew install skagedal/formulae/xcode-simulator-tool
+```
+
+### Using Mint
+
+[Mint] is a pretty nice package manager for Swift Package Manager-based projects, such as this one. 
+
+```bash
+$ mint install skagedal/xcode-simulator-tool
+```
+
+## Development
+
+If you'd like to hack on `xcode-simulator-tool`, you may run `generate-xcodeproj.sh` to generate an Xcode project. 
+
+## Acknowledgements
+
+This tool is largely based on the work of Daniel Cerutti and his [ADVTrustStore] tool.  `xcode-simulator-tool` doesn't do much more than what his tool does at the moment.  I mostly just wanted to rewrite it in Swift.
+
+[ADVTrustStore]: https://github.com/ADVTOOLS/ADVTrustStore
+[Homebrew]: https://brew.sh
+[Mint]: https://github.com/yonaskolb/Mint
+[RootCertificate]: https://en.wikipedia.org/wiki/Root_certificate
+[Swift]: https://developer.apple.com/swift/
+[Xcode]: https://developer.apple.com/xcode/
+
+[swift-badge]: https://img.shields.io/badge/swift-5-orange.svg?style=flat
+[xcode-badge]: https://img.shields.io/badge/xcode-10.2-blue.svg?style=flat