Add metadata

.matharchive.yaml

+Name: "Coq-Packages"
+Url: "https://gl.kwarc.info/jaalbert/coq-packages"
+Version: "8.9.0"
+Structure:
+  SourcePath: "Coq"
+  SourceFiles:
+    - '*.v'
+  ExportPath: "Coq"
+  ExportFiles:
+    - '*.theory.xml'
+    - '*.glob'
+  MmtPath: "content/cic..NONE"
+System:
+  HomepageUrl: "https://coq.inria.fr/packages.html"
+  DocumentationUrl: "https://coq.inria.fr/opam/www/"
+Extras:
+  PackagesFile: "coq-packages.json"
+  PackagesUrl: "https://coq.inria.fr/opam/coq-packages.json"
+