Set 3000 as the default web port

[alagos]

Having by default PORT= only assigns to that variable 0, which is interpreted by puma to start the web app in a random port when bin/dev is called.
Also exporting the port in this file is useless, as in the foreman context, it's eventually overriden by the settings of your default .env file that has just been copied from .env.example.

[alagos]

Worth to mention, I've just started playing with this repo following the setup guide and I faced with the issue where the app was running in a random port every time that I started it (it took me a while to figure out that was because I didn't set the PORT value in the .env file).
For a newcomer as me, will be easier to simply run the app in 3000 instead of trying to figure out where to set this by default (the reason of this PR).

[zachgoll]

@alagos I think we should leave the bin/dev script as-is so that PORT is an optional variable to set in .env

I agree that given the setup instructions, it could be confusing to include PORT=, so definitely willing to accept that change to PORT=3000

[zachgoll]

It's worth mentioning—many of the variables in .env.example are 100% optional to get this app running locally.

The goal with that file is to be a comprehensive overview of all the variables that can be used.

We may just need to specify this a bit more clearly in the dev setup guides as I can see where this would be confusing.

[alagos]

we should leave the bin/dev script as-is so that PORT is an optional variable to set in .env

That's the thing, it doesn't really matter if you call PORT=8080 bin/dev or you change the file to explicitely use

export PORT="8080"

as this script eventually calls foreman, that completely ignores that variable value, as it's already defined in .env.
Might be nice to have just a single place where to set the port and avoid further confusion, but anyway, I've restored the change for bin/dev.