Consider updating README.md to use virtual environments

[mvilain]

The current README instructs users to clone this repo to their systems and install modules required to run sherlock on their systems.

I recommend having users use python's venv virtualize module so their base python3 installation is untouched.

diff --git a/README.md b/README.md
index e6f441a..71505eb 100644
--- a/README.md
+++ b/README.md
@@ -39,8 +39,10 @@ $ git clone https://github.com/sherlock-project/sherlock.git

 # change the working directory to sherlock
 $ cd sherlock
+$ python3 -m venv .

-# install the requirements
+# activate virtual environment and install the requirements
+$ source ./bin/activate
 $ python3 -m pip install -r requirements.txt

[00-kat]

Also, on some Linux distros (I know Arch Linux and OpenSUSE Tumbleweed do this, I think Fedora too), using pip will result in an error saying that you should use your distro's package manager or create a virtual environment.

E.G. on Arch Linux:

error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try 'pacman -S
    python-xyz', where xyz is the package you are trying to
    install.
    
    If you wish to install a non-Arch-packaged Python package,
    create a virtual environment using 'python -m venv path/to/venv'.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip.
    
    If you wish to install a non-Arch packaged Python application,
    it may be easiest to use 'pipx install xyz', which will manage a
    virtual environment for you. Make sure you have python-pipx
    installed via pacman.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.

Edit 2: Also, this wouldn't be as straight-forward as that diff, since on Windows it's .\env\Scripts\activate.{bat,ps1}, and on Linux you need to choose the right file in ./env/bin/ depending on your shell, and source should be . according to POSIX, and some shells might not have a script in ./env/bin/, etc. Not to forget that you can't run .\env\Scripts\activate.ps1 if you don't enable script execution (which is a pain since there's so many ways a simple "paste this in" could go wrong).