DOCS: Update zip name

[AntoninoBonanno]

In the documentation the zip name is my-plugin.zip (<slug>.zip)

wordpress/README.md

Line 44 in e8b42e5

* Create a zip file for the plugin (/tmp/wp-release/my-plugin.zip)

but inside code and test the name of zip is package.zip

wordpress/lib/publish.ts

Lines 20 to 28 in e8b42e5

	const packageResult = await execa(
	zipCommand,
	['-qr', path.join(releaseDir, `package.zip`), config.slug],
	{
	reject: false,
	cwd: config.releasePath,
	timeout: 30 * 1000,
	},
	);

wordpress/test/3-publish-plugin.spec.ts

Line 77 in e8b42e5

expect(files).toContain('package.zip');

and actually the name of the generated zip file is package.zip