Improve README (#514)

Fix some grammar typos.

README.md

@@ -28,7 +28,7 @@ The grape-swagger gem provides an autogenerated documentation for your [Grape](h
 
 ![Demo Screenshot](example/swagger-example.png)
 
-These screenshot is based on the [Hussars](https://github.com/LeFnord/hussars) sample app.
+This screenshot is based on the [Hussars](https://github.com/LeFnord/hussars) sample app.
 
 <a name="related" />
 ## Related Projects
@@ -157,7 +157,7 @@ GrapeSwagger.model_parsers.insert_before(GrapeSwagger::Representable::Parser, Gr
 GrapeSwagger.model_parsers.insert_after(GrapeSwagger::Roar::Parser, GrapeSwagger::Representable::Parser, Representable::Decorator)
 ```
 
-As we know, `Roar::Decorator` uses as superclass `Representable::Decorator`, this allow to avoid problem when Roar objects will be processed by `GrapeSwagger::Representable::Parser`, instead `GrapeSwagger::Roar::Parser`.
+As we know, `Roar::Decorator` uses `Representable::Decorator` as a superclass, this allows to avoid a problem when Roar objects are processed by `GrapeSwagger::Representable::Parser` instead of `GrapeSwagger::Roar::Parser`.
 
 
 ### CORS
@@ -181,7 +181,7 @@ before do
   header['Access-Control-Allow-Origin'] = '*'
   header['Access-Control-Request-Method'] = '*'
 end
-````
+```
 
 
 <a name="configure" />
@@ -204,10 +204,10 @@ end
 
 
 You can pass a hash with optional configuration settings to ```add_swagger_documentation```.
-The examples shows the default value.
+The examples show the default value.
 
 
-The `host` and `base_path` options also accept a `proc` or `lambda` to evaluate, which is passed a [request](http://www.rubydoc.info/github/rack/rack/Rack/Request) object:
+The `host` and `base_path` options also accept a `proc` or a `lambda` to evaluate, which is passed a [request](http://www.rubydoc.info/github/rack/rack/Rack/Request) object:
 
 ```ruby
 add_swagger_documentation \
@@ -388,7 +388,7 @@ add_swagger_documentation \
 * [Swagger Header Parameters](#headers)
 * [Hiding an Endpoint](#hiding)
 * [Overriding Auto-Generated Nicknames](#overriding-auto-generated-nicknames)
-* [Defining an endpoint as array](#array)
+* [Defining an endpoint as an array](#array)
 * [Using an options hash](#options)
 * [Specify endpoint details](#details)
 * [Overriding param type](#overriding-param-type)
@@ -446,9 +446,9 @@ desc 'Get a full list of pets', nickname: 'getAllPets'
 
 
 <a name="array" />
-#### Defining an endpoint as array
+#### Defining an endpoint as an array
 
-You can define an endpoint as array by adding `is_array` in the description:
+You can define an endpoint as an array by adding `is_array` in the description:
 
 ```ruby
 desc 'Get a full list of pets', is_array: true