Complete concept descriptions

[loziniak]

Complete empty introduction.md, about.md and links.json files.

• basics
• blocks
• conditionals
• evaluation
• functions
• none
• script
• strings

[loziniak]

There's some work started on it:
#78

Probably work on concepts should be moved to separate branch, because we don't want to release this track with empty concepts. We should remove all concepts from directory and config on branch main, as well as references to them from practice exercises' practices and prerequisites lists in track's config.json.