mlgpx: restore url file, thanks @hannesm

Author: avsm

packages/mlgpx/mlgpx.1.0.0/opam

@@ -39,3 +39,10 @@ build: [
 ]
 x-maintenance-intent: ["(latest)"]
 dev-repo: "git+https://tangled.sh/@anil.recoil.org/ocaml-gpx"
+url {
+  src: "https://www.cl.cam.ac.uk/~avsm2/distrib/mlgpx-1.0.0.tbz"
+  checksum: [
+    "md5=5342bb7e601273245a9fe263e5a08770"
+    "sha512=cd73b16e988b3ed3cc427a6c6c6d6c9c745adb1eb7efaae3c34e8d006e9c03d9f9d2616cd4118564bd9873903969d3e4053b585e79dbd3e3e7d0f541e2faac83"
+  ]
+}