opam: add page (#3465)

pages/common/opam.md

@@ -0,0 +1,37 @@
+# opam
+
+> OCaml Package Manager.
+> Manage OCaml compilers, tools and libraries.
+> More information: <https://opam.ocaml.org/>.
+
+- Initialize opam for first use:
+
+`opam init`
+
+- Search for packages:
+
+`opam search {{package_name}}`
+
+- Install a package and all of its dependencies:
+
+`opam install {{package_name}}`
+
+- Display detailed information about a package:
+
+`opam show {{package_name}}`
+
+- List all installed packages:
+
+`opam list`
+
+- Update the local package database:
+
+`opam update`
+
+- Upgrade all installed packages:
+
+`opam upgrade`
+
+- Display all commands:
+
+`opam help`