Clarifying / untangling if-else commands in "Linking your default browser to Ubuntu"

[lislis]

Some students seem a little confused with the if-else structure of the browser commands, probably because it's already programming lingo.
What they do is copy all the commands and end up with several export $BROWSER statements in their .zshrc and usually the the wrong one going last and overwriting the rest.
Maybe there is a way to formulate that they should either one or the other but definitely only run one?

[dmilon]

Hi @lislis 👋

There is definitely something to improve about how we define the BROWSER environment variable and how we persist it after the dotfiles repo fork & clone. I'm going to have a look into updating the install.sh ASAP.

Related to #303