Adding some README information on how to consume this example

I also added some cross references to the documentation and blogs where I could find the relevant information.

Signed-off-by: Clebert Suconic <clebertsuconic@apache.org>

README.md

@@ -9,6 +9,31 @@
 The example plugin prints "example" on every query that go handled by the server. It serves as
 documentation for writing CoreDNS plugins.
 
+## Compilation
+
+This package will always be compiled as part of CoreDNS and not in a standalone way. It will require you to use `go get` or as a dependency on [plugin.cfg](https://github.com/coredns/coredns/blob/master/plugin.cfg).
+
+The [manual](https://coredns.io/manual/toc/#what-is-coredns) will have more information about how to configure and extend the server with external plugins.
+
+A simple way to consume this plugin, is by adding the following on [plugin.cfg](https://github.com/coredns/coredns/blob/master/plugin.cfg), and recompile it as [detailed on coredns.io](https://coredns.io/2017/07/25/compile-time-enabling-or-disabling-plugins/#build-with-compile-time-configuration-file).
+
+~~~
+example:github.com/coredns/example
+~~~
+
+After this you can compile coredns by:
+
+```shell script
+go generate
+go build
+```
+
+Or you can instead use make:
+
+```shell script
+make
+```
+
 ## Syntax
 
 ~~~ txt