Automatic installation on ArchLinux

[cphyc]

I have created a package so that the plugin can be easily installed on ArchLinux.

This can be achieved by running yay -S zotero-extension-ocr (see https://aur.archlinux.org/packages/zotero-extension-ocr). Should this be mentioned in the installation doc?

[haverholm]

I only saw this after I had already installed Tesseract, but it worked like a charm to install the poppler dependency. Good work, should absolutely be added to the documentation!

[zuphilip]

Thank you very much. I am happy to accept a PR for adding this (also I am not very active here anymore).

[stweil]

@cphyc, do you want to improve the documentation and send a pull request?