gcd-and-math.md

+# GCD and Math
+
+https://www.raywenderlich.com/79149/grand-central-dispatch-tutorial-swift-part-1
+
+https://developer.apple.com/videos/play/wwdc2016/720/
+
+https://github.com/SVProgressHUD/SVProgressHUD
+
+
+## You should do the following:
+1. Create a new branch from develop called feature/gcd
+2. Connect a new library `SVProgressHUD` via `CocoaPods`.
+3. Add a new button to `OrganizationInfoViewController` called “Calculate 10000th prime number”. It should calculate 10000th prime number in a background queue (global queue). Upon completion it should output the result in an `UIAlertController`. `SVProgressHUD` should be shown during calculation.
+4. Create a pull request.
+
+*HARDMODE: Write function for determining prime number yourself, without googling. Prime number = простое число.*
+
+
+## You should be able to answer the following questions:
+* What is `GCD` used for?
+* What is main queue?
+* What is the difference between sync and async?
+* Can UI be changed in global queue?