Add Linux .desktop file keywords to package.json

[elcste]

Adding keywords to the Linux .desktop file makes it easier to search and find Thorium without using the application name.

Note: I haven't tried building the Thorium package to confirm this works, but I referred to the electron-builder docs and compared with some other Electron apps' package.json files.

[panaC]

I do not see 'keyword' in the documentation https://www.electron.build/configuration/linux

[elcste]

It says

desktop any | “undefined” - The [Desktop file](https://developer.gnome.org/integration-guide/stable/desktop-files.html.en) entries (name to value).

which I understand as meaning you can add other desktop file entries under that. See for example this comment: https://github.com/electron-userland/electron-builder/issues/4974#issuecomment-631072452

I am very happy to test the CI build to confirm it works or not if you add it :-)

[elcste]

I installed the latest dev version deb package on Ubuntu 22.04, and I can now search "ebook", "epub" etc and find Thorium :100:

[danielweck]

That's great. I only occasionally use Linux (I spent most of my time in the MacOS/Darwin console and tools), I didn't realise that this Linux feature existed :)

[elcste]

@danielweck That was my background too before switching to Linux at home. The Linux desktop app world can be very byzantine!