Adds class documentation written by @joelwalden in #95

ruby.html.markdown

@@ -251,4 +251,56 @@ surround { puts 'hello world' }
 # {
 # hello world
 # }
+
+
+# Define a class with the class keyword
+class Human
+
+     # A class variable. It is shared by all instances of this class.
+    @@species = "H. sapiens"
+
+    # Basic initializer
+    def initialize(name, age=0):
+        # Assign the argument to the "name" instance variable for the instance
+        @name = name
+        # If no age given, we will fall back to the default in the arguments list.
+        @age = age
+    end
+
+    # Basic setter method
+    def name=(name)
+        @name = name
+    end
+
+    # Basic getter method
+    def name
+        @name
+    end
+
+    # A class method; uses self to distinguish from instance methods. (Can only be called on class, not an instance).
+
+    def self.say(msg)
+       puts "#{msg}"
+    end
+
+    def species
+        @@species
+    end
+
+end
+
+
+# Instantiate a class
+jim = Human.new("Jim Halpert")
+
+dwight = Human.new("Dwight K. Schrute")
+
+# Let's call a couple of methods
+jim.species #=> "H. sapiens"
+jim.name #=> "Jim Halpert"
+dwight.species #=> "H. sapiens"
+dwight.name #=> "Dwight K. Schrute"
+
+# Call the class method
+Human.say("Hi") #=> "Hi"
 ```