GitLab

- Remove reference to WSL+VcXsrv (which doesn't work)
- Add note about ARM.
- Add link to "Box blur" on Wikipedia from "unit-area box filter"
- Add note about types.
- Add note about OpenGL for Task 1.

* wip of adding clarifications

* more clarification changes

* added windows clion build instructions

* files overview & a few more ta advice

And trim the CMakeLists.txt