Add a more thorough gem description

binding_of_caller.gemspec

@@ -6,8 +6,15 @@ Gem::Specification.new do |spec|
   spec.authors       = ["John Mair (banisterfiend)"]
   spec.email         = ["jrmair@gmail.com"]
 
-  spec.summary       = %q{Retrieve the binding of a method's caller. Can also retrieve bindings even further up the stack.}
-  spec.description   = spec.summary
+  spec.summary       = %q{Retrieve the binding of a method's caller, or further up the stack.}
+  spec.description   = <<-TXT
+Provides the Binding#of_caller method.
+
+Using binding_of_caller we can grab bindings from higher up the call stack and evaluate code in that context.
+Allows access to bindings arbitrarily far up the call stack, not limited to just the immediate caller.
+
+Recommended for use only in debugging situations. Do not use this in production apps.
+TXT
   spec.homepage      = "https://github.com/banister/binding_of_caller"
   spec.license       = "MIT"
   spec.required_ruby_version = Gem::Requirement.new(">= 2.0.0")