interface: render as markdown document

Change-Id: I885f08dd97f751220e37ea91eeab223298c81b69
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/tools/sdbusplus/interface.py b/tools/sdbusplus/interface.py
index 07663e3..7966425 100644
--- a/tools/sdbusplus/interface.py
+++ b/tools/sdbusplus/interface.py
@@ -26,3 +26,7 @@
             kwargs.pop('signals', []) ]
 
         super(Interface, self).__init__(**kwargs)
+
+    def markdown(self, loader):
+        template = loader.get_template("interface.mako.md")
+        return template.render(interface=self, loader=loader)
diff --git a/tools/templates/interface.mako.md b/tools/templates/interface.mako.md
new file mode 100644
index 0000000..17eb835
--- /dev/null
+++ b/tools/templates/interface.mako.md
@@ -0,0 +1,3 @@
+# ${interface.name}
+
+${interface.description}