Mobile support: Add contextual menu on toolbar icon click (instead of linking to the github)

[lrq3000]

Thank you very much for this awesome extension!

On mobile, there is there are some browsers such as Kiwi which support installing any Chrome extension. The issue is that it does not populate the contextual menu as it does on desktop, hence the only way to interact with extensions on mobile is by clicking on the extension's toolbar icon.

Currently, copy-as-markdown directly redirects to this github repo on click, but a simple solution would be to add a simple menu on icon click that simply displays the same options as the right-click contextual menu + a link to this github.