udpated README

README.md

-# While_lang #
+# While_lang
 
-A lexer, parser, and pretty-printer for a simple language of
-imperative programs, that features while loops and functions.
+A lexer, parser, and pretty-printer for `While_lang`, a simple
+language of imperative programs, that features while loops and
+functions.
+
+In this language, functions are mutually recursive by default, can
+receive zero or any positive number of arguments, and they can produce
+zero or any number of outputs.
+
+There is no global variables, no dynamic allocation, and no data
+structures.
 
 This is a good base to start from if you want to implement prototypes
 of interpreters, compilers, static analyzers, etc.
 
 Please feel free to extend this language in any way you see fit.
 
-# Requirements:
+## Requirements:
 
 - `ocaml` 4.14 or above
 - `dune`
 - `menhir`
 - `make` (optional)
 
-# How to build and test
+## How to build and test
 
 To build the program, either type `make` or `dune build`.
 
@@ -32,7 +40,7 @@ name must have the extension `.prog`.
 To run the tests, type `make test` or `dune test --auto-promote`. This
 will run the tests of the `tests/` folder.
 
-# Structure of the source code:
+## Structure of the source code:
 
 - `README.md`: this file
 - `LICENSE`: license of the source code