docs(snapshot): missing vital info (#11502)

* docs(snapshot): depends on java jdk as well

* docs(snapshot): only works on a retina mac

* docs(snapshot): move explanation out of setup

* docs(snapshot): only for mac

scripts/README.md

@@ -86,11 +86,15 @@ To remove the linked version of `ionic-angular` do `npm rm ionic-angular`, and t
 
 ### Running Snapshot
 
-#### Setup
+Snapshot compares to a base snapshot made on Mac OS with retina screen (2560x1600).
+It does not work for windows, linux, or non retina macs.
 
-1. Install [Protractor](https://angular.github.io/protractor/#/): `npm install -g protractor@2.5.1`
-2. Run `webdriver-manager update`
-3. Export `IONIC_SNAPSHOT_KEY` (get from someone)
+#### Setup (Mac OS X Only)
+
+1. Install Java JDK: `brew cask install java`
+2. Install [Protractor](https://angular.github.io/protractor/#/): `npm install -g protractor@2.5.1`
+3. Run `webdriver-manager update`
+4. Export `IONIC_SNAPSHOT_KEY` (get from someone)
 
 #### Commands