added header docs on readme & inline

Author: Jason Kao

README.md

@@ -9,6 +9,15 @@ Low-level GraphQL client for Go.
 * Use variables and upload files
 * Simple error handling
 
+## Installation
+Make sure you have a working Go environment. To install graphql, simply run:
+
+```
+$ go get github.com/machinebox/graphql
+```
+
+## Usage
+
 ```go
 import "context"
 
@@ -29,6 +38,9 @@ req := graphql.NewRequest(`
 // set any variables
 req.Var("key", "value")
 
+// set header fields
+req.Header.Set("Cache-Control", "no-cache")
+
 // define a Context for the request
 ctx := context.Background()
 

graphql.go

@@ -178,9 +178,29 @@ type graphResponse struct {
 
 // Request is a GraphQL request.
 type Request struct {
-	q      string
-	vars   map[string]interface{}
-	files  []file
+	q     string
+	vars  map[string]interface{}
+	files []file
+
+	// Header mirrors the Header of a http.Request. It contains
+	// the request header fields either received
+	// by the server or to be sent by the client.
+	//
+	// If a server received a request with header lines,
+	//
+	//  Host: example.com
+	//  accept-encoding: gzip, deflate
+	//  Accept-Language: en-us
+	//  fOO: Bar
+	//  foo: two
+	//
+	// then
+	//
+	//  Header = map[string][]string{
+	//    "Accept-Encoding": {"gzip, deflate"},
+	//    "Accept-Language": {"en-us"},
+	//    "Foo": {"Bar", "two"},
+	//  }
 	Header Header
 }