update/missing documentation: brief overview, features and comparison

current README.md does IMHO not give a good brief description of duma itself and for what it's good for.
something like http://duma.sourceforge.net/ is something, i would have in mind.
i'd suggest to insert that page - especially with the bullet points - at the begin of README.md.

above page contains the pdf document http://duma.sourceforge.net/74_75_76_77_78_Debugging_DE.pdf
it's german .. but, i'd think it's a good idea to add this document _somehow_ into this github repo - probably not into the sources .. but unsure how/where. github does also offer sort of homepage - but never tried this.

in addition, that more than outdated sourceforge page does not reference this github repo.
i could check/try, if i can change this.

IMHO there's a too much history - not just in the history section - in the current README.md. This most of that could be outsourced into some separate document, e.g. history.md.

detailed description of the many environment variables is in the README.txt , which mostly was identical to the man page. think, this could be also converted into a .md and referenced from the primary README.md

some linux distribution like debian/ubuntu (https://packages.ubuntu.com/search?suite=default§ion=all&arch=any&lang=en&keywords=duma&searchon=names) come with their own packages of duma. might be worth mentioning - if not already. but not sure what code base the maintainers use. but i know, that they used to apply a bunch of patches!

this repo does also come with the subfolder https://github.com/johnsonjh/duma/tree/master/comparisons
the https://github.com/johnsonjh/duma/blob/master/comparisons/README.txt does refers to a dead page.
following link to the wayback machine could be used:
https://web.archive.org/web/20090204104251/http://www.cs.utexas.edu/users/jpmartin/memCheckers.html

anyway, the comparison is more than outdated.
the progress on linux and gcc in the last decade(s) IMHO makes it necessary to give a simple comparison of duma against at least
* gcc address sanitizer: see https://en.wikipedia.org/wiki/AddressSanitizer and https://github.com/google/sanitizers/wiki/AddressSanitizer
* valgrind with memcheck: see https://valgrind.org/docs/manual/mc-manual.html
* anything free and useful for Windows?