Add installation instruction for the esptool in a Python virtual environment.

[SubOptimal]

To avoid confusion about different ways to call the flashing tool esptool in Linux, the list of possibilities was reduced to two ways. One way to install the tool via the package system of the Linux distribution and the other in a Python virtual environment. Both ways are focusing on users with basic Linux experience. For which we assume to be able to adapt the instructions for their specific setup. For users with less Linux experience the flashing method via the browser should be the preferred way.

[opatut]

Why would you remove the list of possible command names? Different distributions package it under different names, that's why we had that list. I found it rather intutitive to work with :shrug:

we assume to be able to adapt the instructions for their specific setup

This is actually not the case and we had people very confused in the past because they would type the command esptool, then get a bash: command not found: esptool, and then they'd give up instead of trying esptool.py.

I do like the expanded installation instructions.

[opatut]

By the way, esptool.py is canonical:

https://github.com/espressif/esptool/blob/41ceca0a72266960252717b3181389902fd89d55/setup.py#L63

Most distributions do it incorrectly, naming the binary esptool instead of esptool.py in their packages ;(

[SubOptimal]

I re-added the other possible commands.