update readme.

README.md

@@ -19,3 +19,14 @@ the REPL uses nodejs to run in the terminal, but changing that probably wouldn't
 ## language overview
 
 TODO
+
+## implementation-specific special lines
+
+here are the commands that are specific to this REPL:
+
+- `!.exit` exits the REPL.
+- `!.env` prints out all the named functions.
+
+## parentheses
+
+catgirl calculus supports using parentheses to group things. this implementation currently does not support this, thus it is non-compliant.