Replace README terminology with GETTINGSTARTED

Political correctness has in recent years become a important part of the tech industry, and specially for the Django project as #2692 and #2694 have proven. Because [other](https://www.drupal.org/node/2275877) projects are now also considering to follow Django's example, I believe it is important for Django to be pro-active in this area.

Due the above stated reasons, I hereby propose renaming Django's `README.rst` file to `GETTINGSTARTED.rst`. The term "readme" can be considered insulting, taunting, and bullying towards any person who can not read.

By getting rid of the "README" terminology, the Django project would be further proving that political correctness is an important topic that is taken seriously.