Write missing TRY_THIS.md for Level 1+ projects

[travisjneuman]

Level 00 exercises each have a TRY_THIS.md with extension prompts. Levels 1+ projects don't have these yet. Create TRY_THIS.md files for Level 1 projects (15 files).

Format: 2-3 extension challenges per file, building on the project's focus area.

[travisjneuman]

Resolved in 36dceb1: Created TRY_THIS.md files for all 15 Level 1 projects with 3 extension challenges each, following the same format as Level 00.