Add comment about samples order. (#3642)

prompb/remote.pb.go

@@ -128,6 +128,7 @@ func (m *Query) GetMatchers() []*LabelMatcher {
 }
 
 type QueryResult struct {
+	// Samples within a time series must be ordered by time.
 	Timeseries []*TimeSeries `protobuf:"bytes,1,rep,name=timeseries" json:"timeseries,omitempty"`
 }
 

prompb/remote.proto

@@ -38,5 +38,6 @@ message Query {
 }
 
 message QueryResult {
+  // Samples within a time series must be ordered by time.
   repeated prometheus.TimeSeries timeseries = 1;
 }