doc: add "The go command" article based on Russ' mail

This is a philosophical document. We can soup it up at a later stage,
but for now it's nice to have a URL to point to that isn't a mailing
list post.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5676061

doc/docs.html

@@ -112,6 +112,7 @@ Guided tours of Go programs.
 <h3>Tools</h3>
 
 <ul>
+<li><a href="/doc/articles/go_command.html">About the Go command</a> - why we wrote it, what it is, what it's not, and how to use it.</li>
 <li><a href="http://blog.golang.org/2011/03/c-go-cgo.html">C? Go? Cgo!</a> - linking against C code with <a href="/cmd/cgo/">cgo</a>.</li>
 <li><a href="http://blog.golang.org/2011/03/godoc-documenting-go-code.html">Godoc: documenting Go code</a> - writing good documentation for <a href="/cmd/godoc/">godoc</a>.</li>
 <li><a href="http://blog.golang.org/2011/06/profiling-go-programs.html">Profiling Go Programs</a></li>