Design `Basic style guide`

[lenucksi]

We should develop an initial version of a basic style guide, which will be used to validate patterns against the requirements of Level 2 - Structured. This is a follow up on PR #155.

(Edited by @maxcapraro)

[spier]

A Basic style guide is now available at
https://github.com/InnerSourceCommons/InnerSourcePatterns/blob/main/meta/pattern-style-guide.md