mgnl-add-availability has the following synopsis:

mgnl-add-availability <[refId/]componentName> <[moduleName:relPath/]page@area> [options]

• The component to add can be from the current module or from any module, npm-cli will not check whether the specified component exists.
• The page to add the component to must exist in the pages dir. of the current folder or in a pages dir of the directory specified by the -p option.

This said, the 2nd argument how it is explained in the synopis can be simplified. And indeed:
mgnl add-availability components/c1 pages/p1@main
results in the same as
mgnl add-availability components/c1 mymodule:pages/p1@main
Since the npm-cli already works correct for both cases, we prbly. just have to adapt the Usage text.

The same is true for the -a option when calling create-component:
both
mgnl create-component c3 -a pages/p1@main
and
mgnl create-component c3 -a my-module:pages/p1@main
does the same.