[Tutorial] the first draft of on-ramp tutorial (for HLSL and GLSL users)

[jkwak-work]

We need tutorial documents for people who are familiar with HLSL or GLSL but not Slang.

Specifically we need to fill in the TODO sections in a commit.

There are multiple "TODO" lines in the commit. This issue is for the following sections:

• docs/coming-from-glsl.md
• docs/coming-from-hlsl.md