copyright: add Loongson into AUTHORS

Contributors to the loong64 port are:
  Weining Lu <[email protected]>
  Lei Wang <[email protected]>
  Lingqin Gong <[email protected]>
  Xiaolin Zhao <[email protected]>
  Meidan Li <[email protected]>
  Xiaojuan Zhai <[email protected]>
  Qiyuan Pu <[email protected]>
  Guoqi Chen <[email protected]>

This port has been updated to Go 1.15.6:
  https://github.com/loongson/go

Updates golang#46229

Change-Id: I23fb430f1f6e8a587f13e2f020721cbd3a45d4ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/342303
Reviewed-by: Ian Lance Taylor <[email protected]>
Trust: Cherry Mui <[email protected]>

AUTHORS

@@ -829,6 +829,7 @@ Liberty Fund Inc
 Linaro Limited
 Lion Yang <[email protected]>
 Lloyd Dewolf <[email protected]>
+Loongson Technology Corporation Limited
 Lorenzo Masini <[email protected]>
 Lorenzo Stoakes <[email protected]>
 Luan Santos <[email protected]>