Update README.md

Author: dylanmckay

README.md

@@ -1,6 +1,9 @@
 # avr-llvm
 
 This repository has been merged into [upstream llvm](http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AVR/).
+Development now occurs directly in LLVM trunk, while this repository exists here solely as an archive of old work and issues.
+
+At this point in time, no changes or commits are added or otherwise backported to this repository.
 
 In order to compile stock LLVM will AVR support enabled, `-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=AVR` must be passed to CMake.
 
@@ -25,3 +28,10 @@ make
 
 Once this is done, you will have a number executables in `build/bin`.
 
+## Viewing the historic avr-llvm fork
+
+This repository contains a few years of development issues, pull requests, and branches prior to the merge of the backend into LLVM trunk.
+
+The old development branch is named [`avr-support`](https://github.com/avr-llvm/llvm/tree/avr-support).
+
+There is a [`master`](https://github.com/avr-llvm/llvm/tree/master) branch that points to the upstream LLVM commit that `avr-support` is based on.