docs: Update godoc for default values (#1665)

This updates the godoc for the following:

ValueThreshold based on #1664
stream.NumGo based on #1593

options.go

@@ -387,7 +387,7 @@ func (opt Options) WithMaxLevels(val int) Options {
 // ValueThreshold sets the threshold used to decide whether a value is stored directly in the LSM
 // tree or separately in the log value files.
 //
-// The default value of ValueThreshold is 1 KB, but LSMOnlyOptions sets it to maxValueThreshold.
+// The default value of ValueThreshold is 1 MB, but LSMOnlyOptions sets it to maxValueThreshold.
 func (opt Options) WithValueThreshold(val int64) Options {
 	opt.ValueThreshold = val
 	return opt

stream.go

@@ -47,7 +47,7 @@ type Stream struct {
 	// iterate over the entire DB.
 	Prefix []byte
 
-	// Number of goroutines to use for iterating over key ranges. Defaults to 16.
+	// Number of goroutines to use for iterating over key ranges. Defaults to 8.
 	NumGo int
 
 	// Badger would produce log entries in Infof to indicate the progress of Stream. LogPrefix can