sg: add page (#11445)

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>
Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/common/sg.md

@@ -0,0 +1,20 @@
+# sg
+
+> Ast-grep is a tool for code structural search, lint, and rewriting.
+> More information: <https://ast-grep.github.io/guide/introduction.html>.
+
+- Scan for possible queries using interactive mode:
+
+`sg scan --interactive`
+
+- Rewrite code in the current directory using patterns:
+
+`sg run --pattern '{{foo}}' --rewrite '{{bar}}' --lang {{python}}`
+
+- Visualize possible changes without applying them:
+
+`sg run --pattern '{{useState<number>($A)}}' --rewrite '{{useState($A)}}' --lang {{typescript}}`
+
+- Output results as JSON, extract information using `jq` and interactively view it using `jless`:
+
+`sg run --pattern '{{Some($A)}}' --rewrite '{{None}}' --json | jq '{{.[].replacement}}' | jless`