Use "The Authors of M2" in citation info

Also add "message" field to CITATION.cff (needed for validation)

[ci skip]

Author: d-torrance

CITATION.cff

@@ -1,10 +1,8 @@
 ---
 cff-version: 1.2.0
+message: If you use Macaulay2 in your research, please cite it as below.
 authors:
-  - family-names: Grayson
-    given-names: Daniel R.
-  - family-names: Stillman
-    given-names: Michael E.
+  - name: The Authors of M2
 title: Macaulay2, a software system for research in algebraic geometry
 url: https://macaulay2.com/
 

M2/Macaulay2/packages/PackageCitations.m2

@@ -208,7 +208,7 @@ iCite String := S -> (
     if S === "M2" then return (
         concatenate (
             "@misc{M2,\n",
-            "  author = {Grayson, Daniel R. and Stillman, Michael E.},\n",
+            "  author = {{The Authors of} M2},\n",
             "  title = {Macaulay2, a software system for research in algebraic geometry},\n",
             "  howpublished = {Available at ", ///\///, "url{https://macaulay2.com/}}\n",
             "}\n",