Update documentation

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

CONTRIBUTING.md

@@ -51,3 +51,31 @@ All our issues are regularly tagged so that you can also filter down the issues
 * If your patch is not getting reviewed or you need a specific person to review it, you can @-reply a reviewer asking for a review in the pull request or a comment, or you can ask for a review on IRC channel [#prometheus](https://webchat.freenode.net/?channels=#prometheus) on irc.freenode.net (for the easiest start, [join via Riot](https://riot.im/app/#/room/#prometheus:matrix.org)).
 
 * Add tests relevant to the fixed bug or new feature.
+
+## Dependency management
+
+The Prometheus project uses [Go modules](https://golang.org/cmd/go/#hdr-Modules__module_versions__and_more) to manage dependencies on external packages. This requires a working Go environment with version 1.11 or greater installed.
+
+All dependencies are vendored in the `vendor/` directory.
+
+To add or update a new dependency, use the `go get` command:
+
+```bash
+# Pick the latest tagged release.
+go get example.com/some/module/pkg
+
+# Pick a specific version.
+go get example.com/some/module/pkg@vX.Y.Z
+```
+
+Tidy up the `go.mod` and `go.sum` files and copy the new/updated dependency to the `vendor/` directory:
+
+
+```bash
+# The GO111MODULE variable can be omitted when the code isn't located in GOPATH.
+GO111MODULE=on go mod tidy
+
+GO111MODULE=on go mod vendor
+```
+
+You have to commit the changes to `go.mod`, `go.sum` and the `vendor/` directory before submitting the pull request.

README.md

@@ -57,7 +57,7 @@ Prometheus will now be reachable at http://localhost:9090/.
 ### Building from source
 
 To build Prometheus from the source code yourself you need to have a working
-Go environment with [version 1.10 or greater installed](http://golang.org/doc/install).
+Go environment with [version 1.11 or greater installed](http://golang.org/doc/install).
 
 You can directly use the `go` tool to download and install the `prometheus`
 and `promtool` binaries into your `GOPATH`:

web/ui/doc.go

@@ -15,7 +15,7 @@
 package ui
 
 import (
-	// The blank import is to make govendor happy.
+	// The blank import is to make Go modules happy.
 	_ "github.com/shurcooL/vfsgen"
 )