Fix some issues with RST readme.

Author: jeromekelleher

README.rst

@@ -1,12 +1,9 @@
 
-Compression utilities for tree sequences.
+Gzip-like compression for tskit tree sequences.
 
 Tszip is a command line utility and Python library for converting the
 ``.trees`` files used by `tskit <https://tskit.readthedocs.org/en/stable/>`_
 into a highly compressed format. Please see the
-`documentation <https://tszip.readthedocs.org/en/stable/installation.html>`_
-for more details.
-
-Please see the
-`installation instructions <https://tszip.readthedocs.org/en/stable/installation.html>`_
-to get started quickly.
+`documentation <https://tszip.readthedocs.org/en/stable>`_
+for more details and
+`installation instructions <https://tszip.readthedocs.org/en/stable/installation.html>`_.