Add logical operators to Ruby tutorial

ruby.html.markdown

@@ -60,8 +60,6 @@ false.class #=> FalseClass
 # Inequality
 1 != 1 #=> false
 2 != 1 #=> true
-!true  #=> false
-!false #=> true
 
 # apart from false itself, nil is the only other 'falsey' value
 
@@ -75,6 +73,17 @@ false.class #=> FalseClass
 2 <= 2 #=> true
 2 >= 2 #=> true
 
+# Logical operators
+true && false #=> false
+true || false #=> true
+!true #=> false
+
+# Alternate spellings of logical operators
+true and false #=> false
+true or false #=> true
+not true #=> false
+
+
 # Strings are objects
 
 'I am a string'.class #=> String