Merge pull request #22 from benbowler/master

Add documentation

README.md

@@ -3,6 +3,20 @@
 [![License](https://img.shields.io/badge/license-MIT-green.svg?style=flat)](LICENSE)
 [![PRs welcome!](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](CONTRIBUTING.md)
 
+## Getting Started
+
+First, generate your signing certificates in the Xcode preferences. Click on the Accounts tab, select your user account and click Manage Certificates. Click the plus button and add the relevant certificates for the type of app you are developing.
+
+Next, create a .p12 file that combines all of your certificates and private keys using [these instructions](https://calvium.com/how-to-make-a-p12-file/). 
+
+Copy the .p12 format in base64:
+
+```
+base64 CertificateFile.p12 | pbcopy
+```
+
+Paste the output of the above command into a secret called `CERTIFICATES_P12` and the password into `CERTIFICATES_P12_PASSWORD` into the GitHub Actions Secrets in the GitHub settings.
+
 ## Usage:
 
 ```yaml
@@ -12,6 +26,10 @@ with:
   p12-password: ${{ secrets.CERTIFICATES_P12_PASSWORD }}
 ```
 
+## Multiple Certificates
+
+If you need to add multiple certificates, select them all in the keychain when creating your p12 file. You do not need multiple separate steps.
+
 ## Additional Arguments
 
 See [action.yml](action.yml) for more details.