Update CMakeLists to avoid warning of mis-matching arguments

- 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.

Tested, merging this for now. Found some related conversation here though: http://cmake.3232098.n2.nabble.com/To-quote-path-variables-or-not-and-everywhere-td7596380.html

* wip of adding clarifications

* more clarification changes

* added windows clion build instructions

* files overview & a few more ta advice

Typo fix: top-left

Typo fix: File does not exist

Fix Visual Studio download link

And trim the CMakeLists.txt