Warn users about 1.6.10

I don't think I'll make a release to work around the bugs at this stage as supposedly there will be a 1.6.11 and it's going to need some testing with the LTO plugin in the new gcc version, the avrdude.conf may need replacing as well for the atmega8 series to maintain compatability.

https://github.com/arduino/Arduino/issues/5168
SpenceKonde/ReleaseScripts#9

I really wish Arduino.cc would get a proper release plan in place, you can't just dump out totally untested major releases on the public, at least have some sort of beta program.  This is ridiculous.

Author: sleemanj

dists/README.md

@@ -1,3 +1,10 @@
+:warning: :warning: :warning: DO NOT USE ARDUINO IDE 1.6.10 :warning: :warning: :warning:
+===
+
+Due to (as is not uncommon) serious bugs in the 1.6.10 Release of the Arduino IDE, **DO NOT** use any of the distribution below with that version of the IDE. Using IDE version 1.6.9 is recommended, do not use 1.6.10 which is more broken than a very broken thing on breaking things day.
+
+Now, read on.
+
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