[doc] add tutorial pages

[HerringtonDarkholme]

Introduction:

1. introduction to ast-grep
2. Why you need structural search
3. what is ast? what is parser? how computer parse your code text
4. introduction to tree-sitter

Basic:

1. simple pattern
2. multi-nodes match $$$
3. simple rule
4. simple kind
5. simple regex
6. simple relational rule with stopBy: end
7. use and / any / not
8. use fix

Intermediate:

1. Refine your pattern: pattern with context
2. Refine your relational rule: stopBy & field
3. utility rule: reusable ast-grep rule
4. constraints: a simple way to constrain how metavar matches
5. Use sgconfig to setup project
6. use sg test to test your rules
7. use ast-grep vscode and lsp
8. use ast-grep playground to develop your rule
9. how to develop and debug rule
10. use ast-grep with AI

Advanced:

1. Refine your pattern II: understand pattern syntax
2. Refine your pattern III: understand how ast-grep matches and strictness
3. utility rule II: recursion (use recursion to munch nodes)
4. use fix II: expand your fix area
5. transform: rewrite metavar
6. transfomr II: rewriter for more advanced manipulation
7. customize matched label
8. ast-grep API usage
9. use ast-grep CLI as a tool: JSON mode and stdin mode
10. use custom language
11. handling embedded code: languageInjection
12. ast-grep limitation and decision tree
    no language specific stuff like macro
    no static analyssi