docs: add a description of the hook

Signed-off-by: monkey92t <golang@88.com>

internal/once.go

@@ -32,7 +32,9 @@ type Once struct {
 
 // Do calls the function f if and only if Do has not been invoked
 // without error for this instance of Once.  In other words, given
-// 	var once Once
+//
+//	var once Once
+//
 // if once.Do(f) is called multiple times, only the first call will
 // invoke f, even if f has a different value in each invocation unless
 // f returns an error.  A new instance of Once is required for each
@@ -41,7 +43,8 @@ type Once struct {
 // Do is intended for initialization that must be run exactly once.  Since f
 // is niladic, it may be necessary to use a function literal to capture the
 // arguments to a function to be invoked by Do:
-// 	err := config.once.Do(func() error { return config.init(filename) })
+//
+//	err := config.once.Do(func() error { return config.init(filename) })
 func (o *Once) Do(f func() error) error {
 	if atomic.LoadUint32(&o.done) == 1 {
 		return nil