Add install steps

Author: Gerry Manoim

README.rst

@@ -7,6 +7,47 @@
 
 Utilities for writing C++ extension modules for CPython.
 
+Install
+-------
+
+lipy supports:
+
+- macOS/Linux
+- Python >=3.5
+
+lipy requires:
+
+- gcc>=8 or clang>=10
+- numpy>=1.11.3
+
+libpy also depends on:
+
+- pcre
+- google sparsehash
+
+To install these dependencies:
+
+**ubuntu**
+
+.. code-block:: bash
+
+    $ sudo apt install libpcre2-dev libsparsehash-dev
+
+**macOS**
+
+.. code-block:: bash
+
+    $ brew install pcre2 google-sparsehash
+
+To install for development:
+
+.. code-block:: bash
+
+   $ make
+
+Otherwise, ``pip install libpy``, making sure ``CC`` and ``CXX`` environment variables are set to the the right compiler.
+
+
 tests
 -----