doc: elaborate available checks for cmd/vet

R=golang-dev, r, ality, r
CC=golang-dev
https://golang.org/cl/5709053

src/cmd/vet/doc.go

@@ -4,18 +4,42 @@
 
 /*
 
-Vet does simple checking of Go source code.
+Vet examines Go source code and reports suspicious constructs, such as Printf
+calls whose arguments do not align with the format string. Vet uses heuristics
+that do not guarantee all reports are genuine problems, but it can find errors
+not caught by the compilers.
 
-It checks for simple errors in calls to functions named
+Available checks:
+
+1. Printf family
+
+Suspicious calls to functions in the Printf familiy, including any functions
+with these names:
 	Print Printf Println
 	Fprint Fprintf Fprintln
 	Sprint Sprintf Sprintln
 	Error Errorf
 	Fatal Fatalf
+	Panic Panicf Panicln
 If the function name ends with an 'f', the function is assumed to take
 a format descriptor string in the manner of fmt.Printf. If not, vet
 complains about arguments that look like format descriptor strings.
 
+It also checks for errors such as using a Writer as the first argument of
+Printf.
+
+2. Methods
+
+Non-standard signatures for methods with familiar names, including:
+	Format GobEncode GobDecode MarshalJSON MarshalXML
+	Peek ReadByte ReadFrom ReadRune Scan Seek 
+	UnmarshalJSON UnreadByte UnreadRune WriteByte
+	WriteTo
+
+3. Struct tags
+
+Struct tags that do not follow the format understood by reflect.StructTag.Get.
+
 Usage:
 
 	go tool vet [flag] [file.go ...]