Add code example to ArrayMesh class docs

doc/classes/ArrayMesh.xml

@@ -3,6 +3,23 @@
 	<brief_description>
 	</brief_description>
 	<description>
+		The [code]ArrayMesh[/code] is used to construct a [Mesh] by specifying the attributes as arrays. The most basic example is the creation of a single triangle
+		[codeblock]
+		var vertices = PoolVector3Array()
+		vertices.push_back(Vector3(0,1,0))
+		vertices.push_back(Vector3(1,0,0))
+		vertices.push_back(Vector3(0,0,1))
+		# Initialize the ArrayMesh.
+		var arr_mesh = ArrayMesh.new()
+		var arrays = []
+		arrays.resize(ArrayMesh.ARRAY_MAX)
+		arrays[ArrayMesh.ARRAY_VERTEX] = vertices
+		# Create the Mesh.
+		arr_mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, arrays)
+		var m = MeshInstance.new()
+		m.mesh = arr_mesh
+		[/codeblock]
+		The [code]MeshInstance[/code] is ready to be added to the SceneTree to be shown.
 	</description>
 	<tutorials>
 	</tutorials>