Add the error recovery paper.

Author: ltratt

softdev.bib

@@ -2552,3 +2552,12 @@ @inproceedings{deutsch84efficient
     pages = "297--302",
     doi = 10.1145/800017.800542,
 }
+
+@inproceedings{diekmann20dontpanic,
+    author = "Lukas Diekmann and Laurence Tratt",
+    title = "Don't Panic! {Better}, Fewer, Syntax Errors for {LR} Parsers",
+    booktitle = "ECOOP",
+    year = 2020,
+    month = Jun,
+    doi = {10.4230/LIPIcs.ECOOP.2020.6},
+}