Update installation instructions to fix dependency name

[felipeavilis]

When running apt-get to install dependencies, i got this message:

Package python-virtualenv is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'python-virtualenv' has no installation candidate

The package was installed using the name python3-virtualenv.

Pull Request Checklist

• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fix a bug that prevented receiving messages from other servers." instead of "Move X method from EventStore to EventWorkerStore.".
  • Include 'Contributed by Your Name.' or 'Contributed by @your-github-username.' — unless you would prefer not to be credited in the changelog.
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
• Pull request includes a sign off

[H-Shay]

Looks like you are missing a changelog file, would you mind adding one? Also forgive me if I missed it, but I don't see a signoff either.

[clokep]

Per @H-Shay's review.

[clokep]

This is a trivial documentation change without any other way to fix it.