Workflow for emscripten-forge

[ianthomas23]

Need to create and document a workflow to go from releases of this project through to builds on Emscripten-forge that can be run in cockle and the Jupyterlite terminal.

[ianthomas23]

The initial release of git2cpp is now on emscripten-forge (see https://prefix.dev/channels/emscripten-forge-dev/packages/git2cpp) and is included in the demo deployment of cockle which is on github pages:

When we do a release here it should propagate through to emscripten-forge and eventually the new version will be available on prefix.dev. After that, on the next PR merge in cockle it should be included in the github pages deployment. All this is untested so far...

Still need to document what happens somewhere in this repo.