Simplify INSTALL.md

[eraychumak]

I agree that my contributions are licensed under the Individual Contributor License Agreement V4.0 ("CLA") as stated in https://github.com/igarastudio/cla/blob/main/cla.md

I have signed the CLA following the steps given in https://github.com/igarastudio/cla#signing

---

Hi @dacap,

Here's a quick link to visually preview the changes to INSTALL.md:
https://github.com/eraychumak/aseprite/blob/simplify-install-guide/INSTALL.md

[dacap]

Hi @eraychumak, thanks for your PR. Some comments about this:

1. I'd prefer to keep a .md file that can be read as a txt file, adding tables might make this harder to read as a regular text file.
2. I prefer to keep the table of contents and sections are they are (although we can really find a significant improvement in the organization of the guide)
3. A lot of information/details were lost in the guide which might not be important but I think they make sense to have them (e.g. what is the $HOME/deps/skia dir, etc.)

I'm closing this PR and you can create an issue to talk about any change you're planning in the guide and why do you think it simplifies some specific section. But please don't rewrite the whole guide or send a new PR rewriting the whole guide before asking.

[eraychumak]

Hi @dacap, no worries. I'll do that next time, thank you! 😁