docs: Added Arch Linux commands to contributing guideline and various minor changes

[shirsakm]

I have added the commands to be run on Arch Linux for setting up the project when contributing, and other minor changes.

Here is a list of the changes I have made,

Added Arch Linux commands

Added a step to add a virtual environment

I find this to be an important step as otherwise there could be dependency conflicts which would result in issues being opened, which are unrelated to the project completely. Moreover, it can be hard to diagnose sometimes.

Moved the important note above the poetry install step

The system packages have to be installed before, and having it afterwards can result in it being missed.

Added $ in front of the commands

It is the standard way to represent a bash prompt, and helps distinguish the various commands, improving readability.

Moved the Python version requirement into a note.

Please let me know if there are any issues, or any edits that go against the formatting guidelines.

[shirsakm]

Implements the changes as mentioned in #408

[shirsakm]

Btw, I believe a tag needs to be added for this PR to count towards Hacktoberfest.

[shirsakm]

Just wanted to mention, was the including of the code blocks in the code blocks intended?
Also, the usage of !!! instead of [!NOTE] is certainly an interesting choice, any particular reasons for the change?

[tomlin7]

@shirsakm you might've noticed the mkdocs config in the root directory, /docs/ is deployed using mkdocs here: https://tomlin7.github.io/biscuit/