docs: Link Rustcardium

Partial merge of !303

Documentation/overview.rst

@@ -48,13 +48,15 @@ Pycardium, take a look at the :ref:`pycardium_guide` guide.
 L0dables
 --------
 Next to Pycardium, other bare-metal code can also run on core 1.  For example,
-a Rustcardium or C-cardium.  These l0dables must be compiled using our special
+a `Rustcardium`_ or C-cardium.  These l0dables must be compiled using our special
 linker script and should link against the api-caller library so they can
 interface with the :ref:`epicardium_api`.
 Note: this feature is disabled by default and has to be enabled at build time.
 To do this, run ``bootstrap.sh`` with the option ``-Djailbreak_card10=true``
 and rebuild the firmware as described in :ref:`how_to_build`.
 
+.. _Rustcardium: https://git.card10.badge.events.ccc.de/astro/rust-card10
+
 .. todo::
 
    Provide more details how this works