Add skip and only option instructions to README

Author: mcelicalderon

README.md

@@ -41,15 +41,16 @@ First, you need to mount the gem in the routes file like this
 Rails.application.routes.draw do
   mount_graphql_devise_for 'User', at: 'api/v1', authenticable_type: Types::CustomUserType, operations: {
     login: Mutations::Login
-  }
+  }, skip: [:sign_up]
+end
 ```
 If you used DTA's installer you will have to remove the `mount_devise_token_auth_for`
 line.
 
 Here are the option for the mount method:
 
 1. `at`: Route where the GraphQL schema will be mounted on the Rails server. In the
-example your API will have this two routes `POST /api/v1//graphql_auth` `GET /api/v1//graphql_auth`.
+example your API will have this two routes `POST /api/v1/graphql_auth` and `GET /api/v1/graphql_auth`.
 If no this option is not specified, the schema will be mounted at `/graphql_auth`.
 1. `operations`: Specifying this one is optional. Here you can override default
 behavior by specifying your own mutations and queries for every GraphQL operation.
@@ -62,6 +63,23 @@ our default classes and yielding your customized code after calling `super`, exa
 and an `authenticable` type to every query. Gem will try to use `Types::<model>Type` by
 default, so in our example you could define `Types::UserType` and every query and mutation
 will use it. But, you can override this type with this option like in the example.
+1. `skip`: An array of the operations that should not be available in the authentication schema. All these operations are
+symbols and should belong to the list of available operations in the gem.
+1. `only`: An array of the operations that should be available in the authentication schema. The `skip` and `only` options are
+mutually exclusive, an error will be raised if you pass both to the mount method.
+
+#### Available Operations
+The following is a list of the symbols you can provide to the `operations`, `skip` and `only` options of the mount method:
+```ruby
+:login
+:logout
+:sign_up
+:update_password
+:send_reset_password
+:confirm_account
+:check_password_token
+```
+
 
 ### Configuring Model
 Just like with Devise and DTA, you need to include a module in your authenticable model,