[Feature]: refreshing repo and upgrading after unpacking a bootstrap.

[twaik]

Feature description

Hello.
Discord has a dedicated tag for this (!tag firstrun) with the following text:

After installing Termux and opening it, you should do the following:

1. termux-change-repo (to select a nearby mirror to get updates from):

• SPACE toggles highlighted options;
• ENTER moves to the next screen;
  Choose the first/topmost option on each screen. (If that one fails, try another.)
  2. pkg update && pkg upgrade (to update your package database, then upgrade all packages)
  On each prompt, press y and Enter to install newest versions available
  3. exit (to exit Termux, so you can restart it yourself, all updated!)

Probably it will be good to perform this automatically right after extracting bootstrap zip.

Additional information

There are a lot of users that are having troubles with this. Only some of them come to discord and complain about non-working repos. IMHO it is a good idea to make it work this way out of the box.