Add a FAQ

FAQ.md

@@ -0,0 +1,9 @@
+## Why do I need to check in `vendor/`?
+
+godep's primary concern is to allow you to repeatably build your project. Your
+dependencies are part of that project. Without them it won't build. Not
+committing `vendor/` adds additional external dependencies that are outside of
+your control. In Go, fetching packages is tied to multiple external systems
+(DNS, web servers, etc). Over time other developers or code hosting sites may
+discontinue service, delete code, force push, or take any number of other
+actions that may make a package unreachable.

Readme.md

@@ -10,6 +10,8 @@ This tool assumes you are working in a standard Go workspace, as described in
 http://golang.org/doc/code.html. We expect godep to build on Go 1.4* or newer,
 but you can use it on any project that works with Go 1 or newer.
 
+Please check the [FAQ](FAQ.md) if you have a question.
+
 ## Install
 
 ```console