blog: add rule / file simplification example

[HerringtonDarkholme]

ast-grep/ast-grep#1779

demonstrate:

1. ast-grep scan -r test.yml test.kt
2. randomly delete some statements
3. use ast dump to delete unrelated file content
4. delete unneeded rule
5. repeat 2-4

[HerringtonDarkholme]

Another example

id: some_sqli_rule
language: python
rule:
  pattern: $X.execute($$$)
  has:
    kind: argument_list
    has:
      nthChild: 1
      any:
        - kind: identifier
          pattern: $VAR
        - has:
            stopBy: end
            kind: identifier
            pattern: $VAR
  inside:
    stopBy: end
    kind: module
    has:
      stopBy: end
      kind: assignment
      pattern: $VAR = $$$

something = "value" # If has comment it does catch the vulnerable line

vuln_param = other

x.execute(f"DROP TABLE IF EXISTS {vuln_param}") # Vulnreable