Add INCLUDE statement to include records from other domains (#1219)

docs/_functions/domain/INCLUDE.md

@@ -0,0 +1,23 @@
+---
+name: INCLUDE
+parameters:
+  - domain
+---
+
+Includes all records from a given domain
+
+
+{% include startExample.html %}
+{% highlight js %}
+
+D("example.com!external", REGISTRAR, DnsProvider(R53),
+  A("test", "8.8.8.8")
+);
+
+D("example.com!internal", REGISTRAR, DnsProvider(R53),
+  INCLUDE("example.com!external"),
+  A("home", "127.0.0.1")
+);
+
+{%endhighlight%}
+{% include endExample.html %}