godoc: add page (#2170)

pages/common/godoc.md

@@ -0,0 +1,15 @@
+# godoc
+
+> Show documentation for go packages.
+
+- Display help for package "fmt":
+
+`godoc {{fmt}}`
+
+- Display help for the function "Printf" of "fmt" package:
+
+`godoc {{fmt}} {{Printf}}`
+
+- Serve documentation as a web server on port "6060":
+
+`godoc -http=:{{6060}}`