Merge pull request #228 from dalek-cryptography/update-yoloproofs-readme

Update readme with yoloproofs note

Author: hdevalence

README.md

@@ -32,11 +32,18 @@ This library provides implementations of:
 
 * Online multi-party computation for aggregated constraint system proofs
   (planned future work).
-  
+
 These proofs are implemented using [Merlin transcripts][doc_merlin],
 allowing them to be arbitrarily composed with other proofs without
 implementation changes.
 
+The development roadmap can be found in the
+[Milestones][gh_milestones] section of the [Github repo][gh_repo].
+
+The constraint system API is provided **FOR EXPERIMENTS ONLY**, and must be
+enabled by specifying the `yoloproofs` feature.  It is not covered by semver
+compatibility and is **SUBJECT TO CHANGE WITHOUT NOTICE**.
+
 ## Documentation
 
 The user-facing documentation for this functionality can be [found
@@ -70,12 +77,6 @@ relative speed compared to the fastest implementation.
 This crate also contains other benchmarks; see the *Tests and Benchmarks*
 section below for details.
 
-## WARNING
-
-This code is still research-quality.  It is not (yet) suitable for
-deployment.  The development roadmap can be found in the
-[Milestones][gh_milestones] section of the [Github repo][gh_repo].
-
 ## Example
 
 ```rust
@@ -137,6 +138,10 @@ Run benchmarks with `cargo bench`. This crate uses [criterion.rs][criterion] for
 
 ## Features
 
+The `yoloproofs` feature enables support for rank-1 constraint system proofs.
+It is **UNSTABLE AND UNSUITABLE FOR DEPLOYMENT**, and **PROVIDED FOR TESTING
+ONLY**.
+
 The `avx2_backend` feature enables `curve25519-dalek`'s AVX2 backend,
 which implements curve arithmetic using [parallel
 formulas][parallel_edwards].  To use it for Bulletproofs, the