readme: Update build instructions (#1916)

* Update build instruction

This changes add proper an easy instruction for building.

* Update README.md

README.md

@@ -57,7 +57,12 @@ Caddy binaries have no dependencies and are available for every platform. Get Ca
 customize your build in the browser
 - **[Latest release](https://github.com/mholt/caddy/releases/latest)** for
 pre-built, vanilla binaries
-- **go get** to build from source: `go get github.com/mholt/caddy/caddy` (requires Go 1.8 or newer) - to build with proper version information (required when filing issues), `cd` to the `caddy` folder and use `go get github.com/caddyserver/builds` followed by `go run build.go`.
+
+## Build
+To build from source you need **[Git](https://git-scm.com/downloads)** and **[Go](https://golang.org/doc/install)** (1.8 or newer). Follow these instruction for fast building:
+
+- Get source `go get github.com/mholt/caddy/caddy` and then run `go get github.com/caddyserver/builds`
+- Now `cd` to `$GOPATH/src/github.com/mholt/caddy/caddy` and run `go run build.go`
 
 Then make sure the `caddy` binary is in your PATH.