doc: Add a few DOIs in .sbib files.

* doc/cise-2022/hpc.sbib, doc/reppar-2015/reppar.sbib: Add DOIs.

doc/cise-2022/hpc.sbib

@@ -63,6 +63,7 @@
   (month "August")
   (pages "579--591")
   (year "2015")
+  (doi "10.1007/978-3-319-27308-2_47")
   (booktitle "Euro-Par 2015: Parallel Processing Workshops")
   (author "Ludovic Courtès, Ricardo Wurmus")
   (title "Reproducible and User-Controlled Software Environments in HPC with Guix"))
@@ -87,6 +88,7 @@
   (volume "584")
   (issue "7822")
   (pages "656–658")
+  (doi "10.1038/d41586-020-02462-7")
   (author "Jeffrey M. Perkel")
   (title "Challenge to Scientists: Does Your Ten-Year-Old Code Still Run?"))
 

doc/reppar-2015/reppar.sbib

@@ -8,6 +8,7 @@
   (booktitle "European Lisp Symposium")
   (year "2013")
   (month "June")
+  (doi "10.48550/arXiv.1305.4584")
   (address "Madrid, Spain"))
 
 ;; http://dl.acm.org/citation.cfm?id=2691141&CFID=514978226&CFTOKEN=55834927
@@ -20,6 +21,7 @@ Lmod")
   (booktitle "Proceedings of the First Workshop on HPC User Support
 Tools (HUST`14)")
   (pages "41--51")
+  (doi "10.1109/HUST.2014.8")
   (isbn "978-1-4673-6755-4")
   (location "New Orleans, Louisiana, USA")
   (publisher "IEEE Press")