logger: add note about dropped logs

At least on i.MX8m+ sof-logger output sometimes contains errors
about dropped logs, even with default verbosity settings.
Increasing DMA_TRACE_LOCAL_SIZE helps, so mention that here.

Signed-off-by: Alexander Boehm <[email protected]>

Author: eurofun

developer_guides/debugability/logger/index.rst

@@ -150,6 +150,9 @@ Examples
   file and start reading from position 0 and thus be in sync with the firmware
   when it is resumed.
 
+  Sometimes error messages about dropped logs are printed. If that is a problem,
+  increasing DMA_TRACE_LOCAL_SIZE in the relevant platform.h file can be helpful.
+ 
 Trace filtering
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