Flesh out opam file

With dependencies as detected by dune.

builder.opam

@@ -0,0 +1,29 @@
+opam-version: "2.0"
+maintainer: "Hannes Mehnert <hannes@mehnert.org>"
+authors: ["Hannes Mehnert <hannes@mehnert.org>"]
+homepage: "https://github.com/roburio/builder"
+dev-repo: "git+https://github.com/roburio/builder.git"
+bug-reports: "https://github.com/roburio/builder/issues"
+license: "ISC"
+
+depends: [
+  "ocaml"
+  "asn1-combinators"
+  "bheap"
+  "bos"
+  "cmdliner"
+  "cstruct"
+  "duration"
+  "fmt"
+  "fpath"
+  "logs"
+  "lwt"
+  "ptime"
+  "rresult"
+  "uuidm"
+]
+build: [
+  ["dune" "subst"] {pinned}
+  ["dune" "build" "-p" name "-j" jobs]
+]
+