Add to `Readme.md` details about the environment variable `PUBLISH` for exporting the package

[Tal500]

Describe the problem

It took me couple of hours to understand why npm ci && npm pack doesn't produce a valid NPM package.
After digging into rollup.config.js I have found that you should set the environment variable PUBLISH=1 for having external dependencies be compiled into your package internally.

Describe the proposed solution

I suggest to write on README.md a section about how to export the package to a tarball for global usage, by setting the environment variable PUBLISH=1 and then npm ci && npm pack(or npm install && npm pack).

Alternatives considered

I know that the README.md file states that the recomended way to build locally and use it, is by using npm link.
However as free software it is always advised to tell in the README.md how to build the package for global usage (here it is by tarball).

Importance

nice to have

[Rich-Harris]

Closing as outdated