Merge pull request #123 from hashicorp/f-update-readme-http-headers

README: Update with HTTP header details

Author: vancluever

README.md

@@ -215,11 +215,12 @@ from the URL before going to the final protocol downloader.
 
 ## Protocol-Specific Options
 
-This section documents the protocol-specific options that can be specified
-for go-getter. These options should be appended to the input as normal query
-parameters. Depending on the usage of go-getter, applications may provide
-alternate ways of inputting options. For example, [Nomad](https://www.nomadproject.io)
-provides a nice options block for specifying options rather than in the URL.
+This section documents the protocol-specific options that can be specified for
+go-getter. These options should be appended to the input as normal query
+parameters ([HTTP headers](#headers) are an exception to this, however).
+Depending on the usage of go-getter, applications may provide alternate ways of
+inputting options. For example, [Nomad](https://www.nomadproject.io) provides a
+nice options block for specifying options rather than in the URL.
 
 ## General (All Protocols)
 
@@ -263,6 +264,13 @@ To use HTTP basic authentication with go-getter, simply prepend `username:passwo
 hostname in the URL such as `https://Aladdin:[email protected]/index.html`. All special
 characters, including the username and password, must be URL encoded.
 
+#### Headers
+
+Optional request headers can be added by supplying them in a custom
+[`HttpGetter`](https://godoc.org/github.com/hashicorp/go-getter#HttpGetter)
+(_not_ as query parameters like most other options). These headers will be sent
+out on every request the getter in question makes.
+
 ### S3 (`s3`)
 
 S3 takes various access configurations in the URL. Note that it will also