Add Readme

Signed-off-by: Ahan Malhotra <ahanmalhotra@college.harvard.edu>

Author: Ahan Malhotra

Makefile

@@ -1,6 +1,6 @@
 # Frontend to dune.
 
-.PHONY: default build install uninstall test clean
+.PHONY: default build install uninstall test clean utop
 
 default: build
 
@@ -18,6 +18,7 @@ uninstall:
 
 clean:
 	dune clean
-# Optionally, remove all files/folders ignored by git as defined
-# in .gitignore (-X).
 	git clean -dfXq
+
+utop:
+	dune utop lib

README.md

@@ -0,0 +1,50 @@
+CS51 Utilities
+==
+
+`cs51/utils` contains some useful utilities for problem sets and labs
+throughout CS51. The `Absbook` module will also be referenced
+throughout the course textbook, _Abstraction and Design in
+Computation_.
+
+
+Installation
+--
+The fastest way to install `cs51/utils` is with `opam`:
+
+```
+opam pin add CS51Utils ssh://git@github.com:cs51/utils.git
+```
+
+For more information on `opam pin`, please consult the
+[opam documentation](https://opam.ocaml.org/doc/Usage.html)
+
+The advantage of the opam-based method is that other opam packages can
+depend on this one, and opam will recompile them automatically as
+necessary.
+
+`cs51/utils` can also be installed directly using `make install` and
+uninstalled using `make uninstall`.
+
+
+Tests
+--
+
+Certain parts of `cs51/utils` have unit tests, which can be run with
+```
+$ make test
+```
+
+Using `cs51/utils` in utop
+--
+
+Use `make utop` where DIR if the folder contains the `dune`
+file for a library. For instance, our `sub2` sample library can be
+used as follows:
+
+```ocaml
+$ dune utop sub2/lib
+...
+utop # CS51Utils.Absbook.id 51 ;;
+- : int = 51
+```
+