Add note to composer docs for cross project packages
What does this MR do?
A question came up recently about publishing a Composer package to a project different from where the code resides. We do not currently support this. This is due to the way Composer works in that:
Composer relies on Git repositories for it’s packages, so when you “publish a package” with composer, it is just pointing to a given tag for the project (no files are uploaded). And when you “install a package”, it is just grabbing the repository files directly