doc: Add scaling documentation

[davidkornel]

I've created the initial scaling documentation I included: Why scaling is important in k8s in general? What does scaling mean in stunner in general? What does scaling in/out mean with stunner? And included an example with yamls. Please take a look at it and let me know where and how to enhance

In the meanwhile, I moved all scaling-related writings from the stunner helm documentation. Just left a link there to this doc

[coveralls]

Pull Request Test Coverage Report for Build 4667601520

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 68.928%

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Totals
Change from base Build 4558434521:	0.0%
Covered Lines:	945
Relevant Lines:	1371

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💛 - Coveralls

[davidkornel]

@rg0now could you give another review and merge if you are satisfied? thanks

[rg0now]

I like this version a lot, thanks! Clean and simple. One minor note: we no longer include the Help/License footers in the docs, pls remove. Once it's done, please go ahead and squash-merge. THX!

[davidkornel]

@rg0now can you approve the changes? I cannot merge until there is a change request by you