add upgrade guide for 3.x

UPGRADE-3.0.md

@@ -0,0 +1,35 @@
+# Upgrading from 2.x to 3.x
+
+### Change styles path
+Styles are moved outside of the src directory so these can be excluded.
+
+`@import '~@freshheads/cookie-guard/src/scss/popup';`
+
+becomes:
+
+`@import '~@freshheads/cookie-guard/styles/popup';`
+
+### No longer use src directory
+The src is now typescript, which is no longer published. Use the build by importing `@freshheads/cookie-guard` 
+This is an ES5 build, but we will soon publish an ES2015 build as well.
+
+### Removed onRevoke callback and selector
+The same can be accomplished by making your own selector and calling the cookieConsentStore.
+
+```
+revokeButton.addEventListener('click', () => {
+    cookieGuard.cookieConsentStore.revoke();
+    window.location.reload();
+});
+```
+
+But we recommend no longer using revoke but offer users the ability to change their choice by calling accept or refuse on the cookie consent store. 
+
+`cookieGuard.cookieConsentStore.accept();`
+
+`cookieGuard.cookieConsentStore.refuse();`
+
+
+### Renames of some config parameters
+
+Check the new config for the correct naming