docs: Import documentation from source-code inline comments.

The inline docs (prefixed with /// in .c files) have been converted to
RST format and put in the docs subdirectory.

docs/tutorial/index.rst

@@ -22,6 +22,16 @@ the tutorial through in the order below.
    usb_mouse.rst
    timer.rst
    assembler.rst
+   power_ctrl.rst
+
+Tips, tricks and useful things to know
+--------------------------------------
+
+.. toctree::
+   :maxdepth: 1
+   :numbered:
+
+   pass_through.rst
 
 Tutorials requiring extra components
 ------------------------------------