Minor documentation issue

Review the installation-time claim in the README and the utils/Helpers.sh installation entry point mentioned in the report. Compare the documented estimate with the reported cache download and build times, then update the README so the installation expectations are realistic. Done means the installation documentation no longer promises less than one minute without qualification.

Really just a minor issue regarding installation time.
The README suggests a "less than 1 minute" installation, while:

on a fresh Arch Linux install (installed on a spare SSD just for the purpose of trying Simula),
with nix installed in the official way,
cachix installed in the official way,

launching the installation process initially "hangs" without any feedback (it's doing something, nix-build is using around 50% CPU on 4 cores) for around 8 minutes at the message:

[user@hostname Simula]$ source ./utils/Helpers.sh && installSimula
/home/user/.nix-profile/bin/nix
nix already installed..
/home/user/.nix-profile/bin/cachix
cachix already installed..
Configured https://simula.cachix.org binary cache in /home/user/.config/nix/nix.conf

Message from Simula Contributors.
=================================

In order to show project funders that Simula is useful, 
we anonymously collect the following data:

- Session length
- Number of windows active
- Error logs on crashes

This on a Ryzen 7 2700 with 32GB of RAM, then it finally goes on with saying:

these 9 derivations will be built:
  /nix/store/9qksxy3iglvq1viqaqpr0a4pmd1n2g8f-xwayland-21.1.1.drv
  /nix/store/cmykn1y1i9bg7aqkd0mnbr48yrg9fn66-nixGLIntel.drv
  /nix/store/xv0q6wa32m2nrxbsx8ln9pxc6akhqagf-xvfb-run.drv
  /nix/store/2cnvlmbpk2dyvnk6jd78zv6c5mcl41iq-godot-3.2.drv
  /nix/store/7gr9xyg36fh8smvhq8gjn2h73kfbzi5f-pernosco_submit.drv
  /nix/store/ri3l2wq7azqqi1z4k5d04cqdp2q808yg-midori.drv
  /nix/store/vcpxqinlf913lhjpza5s8p200nwnncqv-i3status.drv
  /nix/store/zirzk4h1z3z5fwh8ys8ajyw3cxhmdcji-xfce4-terminal.drv
  /nix/store/hmcwa7ggi1qalf87j760q8bpdmykcmvq-Simula.drv

(Funny thing - I use xfce4 as my DE, and it's actually running the compilation inside an xfce4-terminal window, yet it wants to compile it again)

Then it downloads 1.3 GB of packages from the cache (thanks cachix).

I'm now in the middle of the compilation of those 9 packages, 25 minutes in from the installSimula command, fortunately it seems that it's using full multiprocessing, so I hope it won't take too long, even if godot is pretty big to compile.

Just downloading 1.3GB of packages took almost 5 minutes, and I have a standard fiber connection.

I just feel that saying "less than 1 minute" is at least misleading, I'd change that to a more realistic time estimation, it's not a nice presentation.