Update the branding document for JS apps

@rgaudin I noticed your discussion of branding elsewhere (e.g. on Kiwix Desktop). I was not aware there was a branding document, and no-one has ever mentioned it to me!

It needs updating as far as the JavaScript apps are concerned.

1. Remove the entry for "Kiwix UWP", and the repo it points to, which no longer exists (the Repo name was changed to kiwix-js-pwa a couple of years ago).
2. We need an entry for "Kiwix PWA", pointing to https://github.com/kiwix/kiwix-js-pwa.
3. We need an entry for "Kiwix Electron", also pointing to https://github.com/kiwix/kiwix-js-pwa.

On the custom apps made with Electron for Linux and Windows ("Wikivoyage by Kiwix" and "WikiMed by Kiwix"), I [consulted about the branding](https://github.com/kiwix/kiwix-js-pwa/issues/35) before I started publishing them (in the Microsoft Store and on GH Releases) around 6 years ago. It was suggested I use the formula "by Kiwix" in the title of the apps. You can see their branding in the MS Store here:

https://apps.microsoft.com/detail/9phjsnp1cz8j
https://apps.microsoft.com/detail/9n5sb90q4jbj

This can't easily be changed now, at least not without unpublishing the apps, and trying to move all users to a new app, which would inevitably disrupt and strand users.

Start by locating the branding document in the kiwix/overview repository and review its entries for Kiwix UWP and the JavaScript apps. Done means removing the obsolete UWP entry, adding Kiwix PWA and Kiwix Electron with the kiwix-js-pwa link, and preserving the existing Electron app branding details.

Written by the indexing model from the issue text.