fix: README files and links

[mariogarridopt]

Fix docs (README):

• Remove broker images;
• Add new screenshot (not bound to other online pages);
• Removes image from "install" call to action, and switch it to text;
• Added install to chrome button.

[valpackett]

Thanks, but I won't add a screenshot directly into the git repo, I'll look into the broken images thing though.

Added install to chrome button

Woah, what?!

Looks like someone's fork that managed to get it working in Chromium, interesting. I do not endorse it in any case (Get Firefox!)