Add an example ast-grep rule (sg scan resources/test/cpython/)

resources/test/fixtures/A001.py

@@ -1,3 +1,6 @@
+import os.path
+import ospath
+from os import path
 import some as sum
 from some import other as int
 

rules/no-os.yml

@@ -0,0 +1,10 @@
+id: C001
+message: Don't import os
+severity: warning
+language: Python
+rule:
+  any:
+    - pattern: import os
+    - pattern: import os.$_
+    - pattern: from os import $_
+    - pattern: from os.$_ import $_

sgconfig.yml

@@ -0,0 +1,2 @@
+ruleDirs:
+  - rules