README: Added call recording section and cautionary note about using same directory for spool dir and output / recording dir

README.md

@@ -463,6 +463,17 @@ Enabling DTMF transcoding (in one of the two ways described above) implicitly en
 `always transcode` for the call and forces all of the audio to pass through the transcoding engine.
 Therefore, for performance reasons, this should only be done when really necessary.
 
+Call recording
+==============
+
+Call recording can be accomplished in one of two ways: 
+
+* The *rtpengine* daemon can write `libpcap`-formatted captures directly (`--recording-method=pcap`);
+
+* The *rtpengine* daemon can write audio frames into a sink in `/proc/rtpengine` (`--recording-method=proc`). These frames must then be consumed within a short period by another process; while this can be any process, the packaged `rtpengine-recording` daemon is a useful ready implementation of a call recording solution. The recording daemon uses `ffmpeg` libraries to implement a variety of on-the-fly format conversion and mixing options, as well as metadata logging. See `rtpengine-recording -h` for details.
+
+**Important note**: The *rtpengine* daemon emits data into a "spool directory" (`--recording-dir` option), by default `/var/spool/rtpengine`. The recording daemon is then configured to consume this using the `--spool-dir` option, and to store the final emitted recordings (in whatever desired target format, etc.) in `--output-dir`. Ensure that the `--spool-dir` and the `--output-dir` are **different** directories, or you will run into problems (as discussed in #81).
+
 The *ng* Control Protocol
 =========================