Document bug and how to reproduce it

STMBUG.md

@@ -0,0 +1,17 @@
+This version of the branch demonstrates the STM bug.
+
+To reproduce, remove the workaround from `Network.GRPC.Util.Concurrency` by defining
+
+```haskell
+atomically :: forall a. STM a -> IO a
+atomically = STM.atomically
+```
+
+and then run with
+
+```
+while (cabal run test-grapesy -- -p earlyTermination3 2>log); do date; done
+```
+
+You should hit the "blocked indefinitely" very quickly (usually already on the
+first run). 

src/Network/GRPC/Util/Concurrency.hs

@@ -82,6 +82,8 @@ wrapThreadBody body = body
 -- TODO: Fix this properly.
 -- TODO: Is 1 guarded attempt enough..? Do we need more..? Unlimited..?
 atomically :: forall a. STM a -> IO a
+atomically = STM.atomically
+{-
 atomically stm = go 1
   where
     go ::
@@ -92,3 +94,4 @@ atomically stm = go 1
 
     run :: IO a
     run = STM.atomically stm
+-}