doc: document the addition of the AVProbeData.mime_type field and it's implications

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

RELEASE_NOTES

@@ -54,6 +54,9 @@
  │ ⚠  Behaviour changes       │
  └────────────────────────────┘
 
+  • IMPORTANT: The new field mime_type was added to AVProbeData.
+    To avoid crashes, make sure to always initialize AVProbeData, e.g. use
+    'AVProbeData pd = { 0 };' instead of 'AVProbeData pd;'.
   • dctdnoiz filter now uses a block size of 8x8 instead of 16x16 by default
   • -vismv option is deprecated in favor of the codecview filter
   • libmodplug is now detected through pkg-config

doc/APIchanges

@@ -95,6 +95,9 @@ API changes, most recent first:
 2014-07-30 - ba3e331 - lavu 52.94.100 - frame.h
   Add av_frame_side_data_name()
 
+2014-07-29 - 80a3a66 / 3a19405 - lavf 56.01.100 / 56.01.0 - avformat.h
+  Add mime_type field to AVProbeData.
+
 2014-07-29 - 31e0b5d / 69e7336 - lavu 52.92.100 / 53.19.0 - avstring.h
   Make name matching function from lavf public as av_match_name().