README.md in configurations-1.1.0 vs README.md in configurations-1.3.0

@@ -110,17 +110,85 @@
   # c.foo = :not_so_foo
   # c.bar.baz = 'oh my cannot configure'
 end
 ```
 
+### Fourth way: Custom asserted or changed values
+
+If you need further assertions or you need to change a value before it gets stored in the configuration, consider passing a block
+
+```
+module MyGem
+  include Configurations
+  configurable :foo do |value|
+
+    # The return value is what gets assigned, unless it is nil,
+    # in which case the original value persists
+    #
+    value + ' ooooh my'
+  end
+  configurable String, bar: :baz do |value|
+
+    # value is guaranteed to be a string at this point
+    #
+    unless %w(bi ba bu).include?(value)
+      raise ArgumentError, 'baz needs to be one of bi, ba, bu'
+    end
+  end
+end
+```
+
+Gives your users:
+
+```
+MyGem.configure do |c|
+  c.foo = 'FOO'
+  c.bar.baz = %w(bi)
+
+  # This would raise the ArgumentError in the block
+  # c.bar.baz = %w(boooh)
+end
+```
+
 Gives you:
 
 ```
-MyGem.configuration.foo #=> 100% String
-MyGem.configuration.bar.baz #=> 100% Array
+MyGem.configuration.foo #=> 'FOO ooooh my'
+MyGem.configuration.bar.baz #=> one of %w(bi ba bu)
 ```
 
+### Configuration Methods
+
+You might want to define methods on your configuration which use configuration values to bring out another value.
+This is what `configuration_method` is here to help you with:
+
+```
+module MyGem
+  include Configurations
+  configurable :foo, :bar
+  configuration_method :foobar do |arg|
+    foo + bar + arg
+  end
+end
+```
+
+Your users do:
+
+```
+MyGem.configure do |c|
+  c.foo = 'FOO'
+  c.bar = 'BAR'
+end
+```
+
+You get:
+
+```
+MyGem.configuration.foobar('ARG') #=> 'FOOBARARG'
+```
+
+
 ### Defaults:
 
 ```
 module MyGem
   include Configurations
@@ -132,10 +200,9 @@
 
 ### Get a hash if you need it
 
 ```
 MyGem.configuration.to_h #=> a Hash
-
 ```
 
 ### Some caveats
 
 The `to_h` from above is along with `method_missing`, `object_id` and `initialize` the only purposely defined method which you can not overwrite with a configuration value.