Document DevTools usage for WebViews (especially on Mac OS)

[Duckwhale]

On Windows (EDGE) and WSL (WebKit2GTK) it seems to be working as expected: Just press F12 and that's it.

On Mac OS, however, there are some hoops to jump through: Keyboard shortcut is the same as in Safari (CMD + ALT + J), which is already odd and apparently cannot be changed? However, the web inspector is also disabled by default outside of Safari, see https://developer.apple.com/forums/thread/4326 for details.

It might also be worth verifying that the inspector actually works in the real Safari browser first?

Symptoms of it not working: Keyboard shortcut only plays error sound, opening via right-click menu bugs out the WebView (white frame where the dev tools should be...).

[Duckwhale]

See https://webkit.org/blog/13936/enabling-the-inspection-of-web-content-in-apps/

Needs setInspectable flag? (See upstream PR 940)