update README.md

README.md

@@ -7,6 +7,25 @@ programming, which is itself written in a high-level language.
 
 ![Scryer Logo: Cryer](logo/scryer.png)
 
+# Rebis Development Branch
+
+![Art Card](logo/art_card.jpg)
+
+This is the Rebis Development Branch (rebis-dev). This iteration of
+Rebis contains sweeping changes to the instruction dispatch loop
+alongside a compacted heap representation. These changes are to
+enhance the performance and robustness of Scryer Prolog and to prepare
+for the introduction of a mark-compacting garbage collector.
+
+Several performance enhancing changes are due before rebis-dev will be
+considered ready for merging into master, among them:
+
+* Replacing choice points pivoting on inlined deterministic predicates
+  (`atom`, `var`, etc) with if/else ladders
+* Inlining all built-ins and system call instructions
+* Greatly reducing the number of instructions used to compile disjunctives
+* Storing short atoms to heap cells without writing them to the atom table
+
 ## Phase 1
 
 Produce an implementation of the Warren Abstract Machine in Rust, done