docs: releases/v2016.2.6: add "Known issues" section

docs/releases/v2016.2.6.rst

@@ -40,3 +40,18 @@ Bugfixes
   server, will be terminated at the start of the sysupgrade to allow unmounting
   the root filesystem. This makes it impossible to get any feedback from the
   upgrade process without a serial console.
+
+Known Issues
+~~~~~~~~~~~~
+
+* Default TX power on many Ubiquiti devices is too high, correct offsets are unknown (`#94 <https://github.com/freifunk-gluon/gluon/issues/94>`_)
+
+  Reducing the TX power in the Advanced Settings is recommended.
+
+* The MAC address of the WAN interface is modified even when Mesh-on-WAN is disabled (`#496 <https://github.com/freifunk-gluon/gluon/issues/496>`_)
+
+  This may lead to issues in environments where a fixed MAC address is expected (like VMware when promicious mode is disallowed).
+
+* Inconsistent respondd API (`#522 <https://github.com/freifunk-gluon/gluon/issues/522>`_)
+
+  The current API is inconsistent and will be replaced eventually. The old API will still be supported for a while.