feat: add a PR-331 video

- Close #165

Author: kkweon

server/internal/data/mapping_table.pbtxt

@@ -2451,3 +2451,10 @@ rows: {
   paper_arxiv_ids: "2012.12877"
   youtube_video_id: "A3RrAIx-KCc"
 }
+rows: {
+  pr_id: 331
+  paper_arxiv_ids: "2106.07998"
+  paper_arxiv_ids: "1706.04599"
+  paper_arxiv_ids: "2106.07998"
+  youtube_video_id: "rI-vJuNKyIU"
+}