Add Tact compiler installation instructions

[anton-trunov]

It would be nice for the docs to be self-contained

[novusnota]

Perhaps so. Although it would also be nice to eventually introduce a "Set up your environment" page or something like that early in the docs, right after the starting page and on top of the Book.

Inspiration:

• https://docs.deno.com/runtime/manual/getting_started/first_steps#configure-your-ide, which points to ->
• https://docs.deno.com/runtime/manual/getting_started/setup_your_environment

[anton-trunov]

I like the idea of adding this kind of stuff to the docs!

There is a related issue already: https://github.com/tact-lang/tact-docs/issues/47