Flashing resources documentation/improvements

Verification

• I searched for similar issues (including closed issues) and found none was relevant.

Introduce the issue

• itd (https://gitea.elara.ws/Elara6331/itd) is currently not working too well due to this issue
• GadgetBridge doesn't yet support uploading resources so without digging into another project and stack I'm unable to upload new resources to my sealed PineTime.
• WatchMate does actually work for uploading resources, however it's not documented on the doc/gettingStarted/updating-software.md page. It's also somewhat unstable (I have to disconnect/reconnect/remove/etc to get a stable Bluetooth connection) and it's also not documented that Infinitime Resources.zip can't be flashed directly, it has to be unzipped into infinitime-resources-1.13.0.zip in order to work. This is distinct from InfiniTime DFU.zip which works just like pinetime-mcuboot-app-dfu-1.13.0.zip.

Preferred solution

It seems like all these things almost work, if someone could give these various items a nudge it'd help greatly.

Version

main

Start with doc/gettingStarted/updating-software.md and compare its existing flashing guidance with the WatchMate workflow described in the issue. Document how InfiniTime Resources.zip differs from InfiniTime DFU.zip, including the required resource archive name, and capture the relevant connection or stability caveats; done means the page covers these steps clearly.