`.SortFlags` documentation could be improved

[jsumners]

pflag/README.md

Lines 250 to 266 in 6fcfbc9

	## Disable sorting of flags
	`pflag` allows you to disable sorting of flags for help and usage message.
	**Example**:
	```go
	flags.BoolP("verbose", "v", false, "verbose output")
	flags.String("coolflag", "yeaah", "it's really cool flag")
	flags.Int("usefulflag", 777, "sometimes it's very useful")
	flags.SortFlags = false
	flags.PrintDefaults()
	```
	**Output**:
	```
	-v, --verbose verbose output
	--coolflag string it's really cool flag (default "yeaah")
	--usefulflag int sometimes it's very useful (default 777)
	```

That documentation indicates that the following should work:

func main() {
  pflag.Bool("foo", false, "Foo should be first")
  pflag.Bool("bar", false, "Bar should be second")
  pflag.SortFlags = false
  pflag.PrintDefaults()
}

But that's not so, because pflag.SortFlags does not exist. It is a member of pflag.FlagSet:

pflag/flag.go

Lines 156 to 164 in 6fcfbc9

	type FlagSet struct {
	// Usage is the function called when an error occurs while parsing flags.
	// The field is a function (not a method) that may be changed to point to
	// a custom error handler.
	Usage func()
	// SortFlags is used to indicate, if user wants to have sorted flags in
	// help/usage messages.
	SortFlags bool

The docs should be updated to show a clearer example that doesn't require deeper knowledge of the module.

[tomasaschan]

The docs for this library could use some love in general - not only is this example a little unclear (it seems to assume that flags is a FlagSet instance, while you seem to assume it's a named import of the pflag package) but the entire Readme is also pretty inconsistent in how examples are presented (some are complete with imports and main method, some are just code snippets that assume a certain setup; that assumed setup is also not consistent across examples; etc...).

PRs to address this are welcome.