Clarify the status of this repo

README.md

@@ -25,3 +25,23 @@ This is a more flexible version of mtl, the monad transformers library.
 
     If you'd like to define your own monad-classes-style class, you have to
     write much less boilerplate code.
+
+## The status of this repo
+
+This repo serves two purposes:
+
+* as a reference implementation accompanying the [series of articles on
+  extensible effects][1]
+* as an actual implementation we use at [Signal Vine](http://signalvine.com/)
+
+While this is technically open source software, I am not interested in maintaining this as
+an active open project. In practice this means that:
+
+* this version of monad-classes is not on hackage
+* I do not accept feature requests and pull requests. The exception is outright
+  bugs; if you find any, please do report them.
+
+There is a [hackage package][2] and a [repo][3] maintained by M Farkas-Dyck.
+
+[2]: https://hackage.haskell.org/package/monad-classes
+[3]: https://github.com/strake/monad-classes.hs