Update documentation for multiple cameras and zoom.

    the standard and ultra-wide camera.

    If Settings/On screen GUI/"Multiple cameras icon" is disabled, then this icon will not show; instead the "Switch camera"

    icon can by used to cycle through all the cameras.

    Note that some devices do not allow third party applications to access their multiple cameras, in which case Open Camera isn't

    Note that some devices do not expose the multiple cameras explicitly, but instead will automatically switch cameras as required

    when zooming in or out (requires Camera2 API).

    Note that some other devices do not allow third party applications to access their multiple cameras at all, in which case Open Camera isn't

    able to use them.</p>

<p><img src="exposure_unlocked.png" alt="Lock Exposure icon" width="32" height="32"><b>Exposure lock</b> - Click to lock or unlock the exposure.

<p><b>Show What's New dialog</b> - When updating to a major new version, Open Camera displays a dialog explaining the new

features and other options. You can disable this dialog from being displayed if you prefer.</p>

<p><b>Multiple cameras icon</b> - This option only shows on devices with more than one front and/or back cameras. When

<p><b>Multiple cameras icon</b> - This option only shows on devices that allow explicitly switching between more than

one front and/or back cameras. When

enabled (the default), such devices will have two on-screen icons: one to switch between front/back cameras, and another

to switch between the multiple front or back cameras. If this option is disabled, only a single icon will show, which

will cycle between all cameras.</p>

that are made available to third party applications. Usually this means front and back cameras, but some devices have

multiple front and/or back-facing cameras. Use the

<img src="baseline_add_a_photo_white_48.png" alt="Switch multi-camera icon" width="16" height="16">switch multi-camera icon

to switch between multiple front or back cameras. In some cases the extra cameras aren't made available to third party

applications, so it isn't possible for Open Camera to support them. Even where they are, since there is no current standard

on what the extra cameras are used for, it can't do anything with them other than allowing you to switch between them.</p>

to switch between multiple front or back cameras. Note that some devices do not expose the multiple cameras explicitly,

but instead will automatically switch cameras as required when zooming in or out. In some cases the extra cameras aren't

made available to third party applications, so it isn't possible for Open Camera to support them.</p>

<p><b>Why doesn't Open Camera support the maximum video resolution on my device?</b> - If you

are using Camera2 API, make sure that you're not in slow motion mode (see "Speed" under