Following developper's guide, beats won't compile

Disclaimer: I am a total noob in Go.

When running from Getting Ready section in Developpers's guide:

go get github.com/elastic/beats

I have the following error:

package github.com/elastic/beats: no buildable Go source files in <GOPATH>/src/github.com/elastic/beats

I succeeded build topbeat by making

go get github.com/elastic/beats/topbeat

After having installed all dependencies (see error trace when trying to built it the first time to know what to go get).

There where also an error concerning sigar/gosigar. I just added "sigar" aliases in topbeat.go (l10) and sigar.go (l8)

we've vendored all dependencies in github.com/elastic/beats repository. You need to run export GO15VENDOREXPERIMENT=1 before running make.

I opened an issue here to add this to the developer guide: https://github.com/elastic/beats/issues/983