README-migration: some improvements to the audio section.

Minor edit about default devices, and an explanation of forcing device buffer
size with SDL_HINT_AUDIO_DEVICE_SAMPLE_FRAMES.

Fixes libsdl-org#9857.

docs/README-migration.md

@@ -179,7 +179,7 @@ SDL_AudioDeviceID now represents both an open audio device's handle (a "logical"
 
 Devices are opened by physical device instance ID, and a new logical instance ID is generated by the open operation; This allows any device to be opened multiple times, possibly by unrelated pieces of code. SDL will manage the logical devices to provide a single stream of audio to the physical device behind the scenes.
 
-Devices are not opened by an arbitrary string name anymore, but by device instance ID (or magic numbers to request a reasonable default, like a NULL string in SDL2). In SDL2, the string was used to open both a standard list of system devices, but also allowed for arbitrary devices, such as hostnames of network sound servers. In SDL3, many of the backends that supported arbitrary device names are obsolete and have been removed; of those that remain, arbitrary devices will be opened with a default device ID and an SDL_hint, so specific end-users can set an environment variable to fit their needs and apps don't have to concern themselves with it.
+Devices are not opened by an arbitrary string name anymore, but by device instance ID (or magic numbers to request a reasonable default, like a NULL string would do in SDL2). In SDL2, the string was used to open both a standard list of system devices, but also allowed for arbitrary devices, such as hostnames of network sound servers. In SDL3, many of the backends that supported arbitrary device names are obsolete and have been removed; of those that remain, arbitrary devices will be opened with a default device ID and an SDL_hint, so specific end-users can set an environment variable to fit their needs and apps don't have to concern themselves with it.
 
 Many functions that would accept a device index and an `iscapture` parameter now just take an SDL_AudioDeviceID, as they are unique across all devices, instead of separate indices into playback and recording device lists.
 
@@ -214,7 +214,7 @@ SDL_QueueAudio(), SDL_DequeueAudio, and SDL_ClearQueuedAudio and SDL_GetQueuedAu
 
 APIs that use channel counts used to use a Uint8 for the channel; now they use int.
 
-SDL_AudioSpec has been reduced; now it only holds format, channel, and sample rate. SDL_GetSilenceValueForFormat() can provide the information from the SDL_AudioSpec's `silence` field. The other SDL2 SDL_AudioSpec fields aren't relevant anymore.
+SDL_AudioSpec has been reduced; now it only holds format, channel, and sample rate. SDL_GetSilenceValueForFormat() can provide the information from the SDL_AudioSpec's removed `silence` field. SDL3 now manages the removed `samples` field; apps that want more control over device latency and throughput can force a newly-opened device's sample count with the SDL_HINT_AUDIO_DEVICE_SAMPLE_FRAMES hint, but most apps should not risk messing with the defaults. The other SDL2 SDL_AudioSpec fields aren't relevant anymore.
 
 SDL_GetAudioDeviceSpec() is removed; use SDL_GetAudioDeviceFormat() instead.