fix opam file and add install steps to README

dune-project

@@ -21,7 +21,19 @@
  (name aoc)
  (synopsis "A short synopsis")
  (description "A longer description")
- (depends ocaml dune)
+ (depends
+   ocaml
+   dune
+   re
+   containers
+   iter
+   dune-site
+   angstrom
+   ppx_deriving
+   ppx_deriving_hash
+   ppx_regexp
+   ppx_expect
+   ppx_inline_test)
  (sites (lib inputs))
  (tags
   (topics "to describe" your project)))