Add Destructuring Arrays In Blocks as a ruby til.

ruby/destructuring-arrays-in-blocks.md

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+# Destructuring Arrays In Blocks
+
+If I am iterating over a collection of arrays (let's say tuples) and I want
+to access the values of those arrays within the iteration block, I may do
+something like the following:
+
+```ruby
+> a = [[1,2],[3,4],[5,6]]
+> a.each { |tuple| puts "#{tuple[0]} - #{tuple[1]}" }
+1 - 2
+3 - 4
+5 - 6
+```
+
+I can, however, use array destructuring which will not only simplify the
+code, but also make it more readable, explicit, and intentional.
+
+```ruby
+> a = [[1,2],[3,4],[5,6]]
+> a.each { |x_coord,y_coord| puts "#{x_coord} - #{y_coord}" }
+1 - 2
+3 - 4
+5 - 6
+```
+
+In the same way, I can destructure arrays that are part of a hash like so:
+
+```ruby
+> h = {one: [1,2], two: [3,4], three: [5,6]}
+> h.each { |key, (x_coord, y_coord)| puts "#{x_coord} - #{y_coord}" }
+1 - 2
+3 - 4
+5 - 6
+```
+
+Note the parentheses that are placed around the part that is being
+destructured. Without these parentheses, ruby will interpret `x_coord` as
+the whole array value and `y_coord` will be `nil`.