Add KB article about testing and logging info from the runtime

[joepetrowski]

[riusricardo]

There is a recipe that @JoshOrndorff will take-over:
JoshOrndorff/substrate-recipes#134

Related to:
JoshOrndorff/substrate-recipes#130

[joepetrowski]

A lot of people are asking in substrate-technical. I think it'd be a good idea to have a page in the docs with all the ways you can print runtime info, and then recipes with more examples. WDYT?

[riusricardo]

SGTM. It is an important feature. It will get more discoverability if we have it in docs and more examples in recipes.

[JoshOrndorff]

I do plan to take over Ricardo's draft PR, but it's worth mentioning that this is already covered in the first Appetizer recipe. https://substrate.dev/recipes/2-appetizers/1-hello-substrate.html#inside-a-dispatchable-call