installation: add note about unsupported locally administered MAC addresses

Author: c-po

docs/installation/index.rst

@@ -2,6 +2,17 @@
 Installation and Image Management
 #################################
 
+.. note:: This is most likely only relevant for virtual installations:
+
+   When installing VyOS ensure that the MAC address selected for your NICs is
+   not a locally administered MAC address. Locally administered addresses are
+   distinguished from universally administered addresses by setting (assigning
+   the value of 1 to) the second-least-significant bit of the first octet of
+   the address:
+
+   Example: ``02:00:00:00:00:01``, where the second-least-significant bit
+   (``02`` in hex) is set to ``1``.
+
 .. toctree::
    :maxdepth: 2
    :caption: Content