Add docs to README pointing to how to build new version (#1)

Adds simple docs found in `kohls_db2ex` to README pointing to how to
build new version.

Co-authored-by: Liam Morley <liam@mechanical-orchard.com>

Author: germsvel

README.md

@@ -3,3 +3,12 @@ This repo distributes Erlang/OTP's jinterface package as a maven package publish
 Erlang/OTP is hosted on [github](https://github.com/erlang/otp), and jinterface is currently located in [this subdirectory](https://github.com/erlang/otp/tree/master/lib/jinterface)
 
 The source it builds from has not been modified.
+
+## Building a new version to target an OTP version
+
+If there is no [published version] for the `OTP_VERSION` you want to
+use, trigger a workflow here:
+
+https://github.com/mechanical-orchard/jinterface/actions/workflows/build.yml
+
+[published version]: https://github.com/orgs/mechanical-orchard/packages?repo_name=jinterface