doc: add merge note for printStatistics + GetStat integration

After merging print-statistics, the printStatistics call site should
pass s.GetStat() instead of s.GetOutput() so :perftrace redirection
applies to performance statistics output.

Author: dlevy-msft-sql

pkg/sqlcmd/sqlcmd.go

@@ -237,7 +237,10 @@ func (s *Sqlcmd) SetError(e io.WriteCloser) {
 	s.err = e
 }
 
-// GetStat returns the io.Writer to use for performance statistics
+// GetStat returns the io.Writer to use for performance statistics.
+// Falls back to GetOutput() when no :perftrace redirection is active.
+// After merging PR #631 (print-statistics), update the printStatistics
+// call site from s.GetOutput() to s.GetStat().
 func (s *Sqlcmd) GetStat() io.Writer {
 	if s.stat == nil {
 		return s.GetOutput()