fix README markdown

README.md

@@ -33,15 +33,15 @@ This repository contains the following case studies:
 * [logrel](theories/logrel): Logical relations from the
   [IPM paper](http://doi.acm.org/10.1145/3093333.3009855):
   - STLC
-    * Unary logical relations proving type safety
+    - Unary logical relations proving type safety
   - F_mu (System F with recursive types)
-    * Unary logical relations proving type safety
+    - Unary logical relations proving type safety
   - F_mu_ref (System F with recursive types and references)
-    * Unary logical relations proving type safety
-    * Binary logical relations for proving contextual refinements
+    - Unary logical relations proving type safety
+    - Binary logical relations for proving contextual refinements
   - F_mu_ref_conc (System F with recursive types, references and concurrency)
-    * Unary logical relations proving type safety
-    * Binary logical relations for proving contextual refinements
+    - Unary logical relations proving type safety
+    - Binary logical relations for proving contextual refinements
       - Proof of refinement for a pair of fine-grained/coarse-grained concurrent
         counter implementations
       - Proof of refinement for a pair of fine-grained/coarse-grained concurrent