add audio source to readme

Author: AlexandreRouma

readme.md

@@ -329,6 +329,7 @@ Modules in beta are still included in releases for the most part but not enabled
 |----------------------|------------|-------------------|--------------------------------|:---------------:|:-----------------------:|:---------------------------:|
 | airspy_source        | Working    | libairspy         | OPT_BUILD_AIRSPY_SOURCE        | ✅              | ✅                     | ✅                         |
 | airspyhf_source      | Working    | libairspyhf       | OPT_BUILD_AIRSPYHF_SOURCE      | ✅              | ✅                     | ✅                         |
+| audio_source         | Working    | rtaudio           | OPT_BUILD_AUDIO_SOURCE         | ✅              | ✅                     | ✅                         |
 | bladerf_source       | Working    | libbladeRF        | OPT_BUILD_BLADERF_SOURCE       | ⛔              | ✅ (not Debian Buster) | ✅                         |
 | file_source          | Working    | -                 | OPT_BUILD_FILE_SOURCE          | ✅              | ✅                     | ✅                         |
 | hackrf_source        | Working    | libhackrf         | OPT_BUILD_HACKRF_SOURCE        | ✅              | ✅                     | ✅                         |