move things around

firmware/doc/_doxygen/groups.dox

@@ -0,0 +1,17 @@
+/**
+ * @defgroup drivers Custom driver classes
+ * @{
+ *
+ * @brief Custom driver classes
+ *
+ * @}
+ */
+
+/**
+ * @defgroup lib Custom libraries
+ * @{
+ *
+ * @brief Custom libraries
+ *
+ * @}
+ */

firmware/doc/_doxygen/main.md

@@ -0,0 +1,5 @@
+# Introduction
+
+This is the Doxygen documentation for [example-application].
+
+[example-application]: https://github.com/zephyrproject-rtos/example-application