Add step-by-step tutorial

[alexyakunin]

I'm thinking of the following approach:

• Root-level "tutorial" folder contains numbered sections (p1_simple_computed, p2_[...], etc.)
• Section = a directory with a single file (or maybe N files, if needed) + readme.md
• Launcher = https://github.com/dotnet/try

[yakunins]

I guess the easy way for any user is to

1. find a link to example's repo
2. checkout example's repo (hello world),
3. compile and run it locally in minimal amount of time

[alexyakunin]

I guess the easy way for any user is to

1. find a link to example's repo
2. checkout example's repo (hello world),
3. compile and run it locally in minimal amount of time

Yes, that's exactly how it works, but Tutorial is still needed.

[alexyakunin]

Done.