Installation instructions in the top-level "README.rst" file has been
truncated to trivial one-liners for simplicity, readability, and parity
with comparable instructions in the same file under BETSE. Specifically,
this commit:

* Documentation revised:
  * Installation instructions rewritten. These instructions have been
    revised from the ground up for simplicity, consistency, and with an
    increased emphasis on the standard pip ecosystem rather than the
    increasingly non-standard Anaconda ecosystem. Specifically:
    * "README.rst" truncated. The top-level "README.rst" file now
      provides only minimal instructions for installing BETSE under the
      two most popular platform-agnostic package managers: pip
      (recommended) and Anaconda.

(Further longings of the longest farthing!)