Add a section or page for medium-use tools

In wiki/Installing_the_Frequently-Used_Programs_for_CME-Lab.md, we have a guide on our most-frequently used software. There are other tools that tend to be useful, but used less frequently. Let's we make a section with links and info for these. For starters, [Avogadro](https://avogadro.cc/) is pretty handy. If there are others you think should be included, please comment below.

Start by reading wiki/Installing_the_Frequently-Used_Programs_for_CME-Lab.md and review how the existing frequently used software is organized. Add a section for less frequently used tools beginning with Avogadro, including its link and useful information; the work is done when the new section is clear and integrated with the guide.

Written by the indexing model from the issue text.