Update 'Control Flow'

Control-Flow.md

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+ARF has a collection of basic control flow phrases which are `break`, `next`,
+and `return`. Break breaks out of a loop or switch case, next is basically just
+a continue statement but using less letters, and a return phrase returns from
+the current function. Return phrases are entirely optional and do not take any
+arguments.
+
+ARF also has some control flow phrases that expect an indented block of phrases
+under them:
+
+```
+if condition
+	something
+
+if condition
+	something
+else
+	otherThing
+
+while condition
+	something
+
+switch value
+: 324
+	something
+: 93284
+	otherThing
+:
+	defaultThing
+
+for index:Size element:Int someArray
+	something
+```
+
+These do what you'd expect them to, but for loops in ARF need some further
+explanation. Many modern languages allow you to iterate over data, and ARF is no
+exception. The first argument of a for loop must be an index of type Size, the
+second argument must be typed as an element of the third argument, which must
+be an array or inherit from an array. In the future there might be some
+iterateable interface that an object could fulfil.