Replace "pip" with "pip3" on linux systems

[ghost]

I recommend replacing only the string when attempting to install some packages on different operating systems.

For example, on windows, installation of a pip package would probably look like this:
pip install package_name

while on Linux, it would be like this:
pip3 install package_name

I think it would save some begginers a lot of time searching for the issue solution, by just finding the operating system of the user, and producing different strings according to that.

[di]

Closing this as a duplicate of #1563, but thanks for the report!