docs: Add section on pySim-trace to user manual
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+pySim-trace
+===========
+
+pySim-trace is a utility for high-level decode of APDU protocol traces such as those obtained with
+`Osmocom SIMtrace2 <https://osmocom.org/projects/simtrace2/wiki>`_ or `osmo-qcdiag <https://osmocom.org/projects/osmo-qcdiag/wiki>`_.
+
+pySim-trace leverages the existing knowledge of pySim-shell on anything related to SIM cards,
+including the structure/encoding of the various files on SIM/USIM/ISIM/HPSIM cards, and applies this
+to decoding protocol traces. This means that it shows not only the name of the command (like READ
+BINARY), but actually understands what the currently selected file is, and how to decode the
+contents of that file.
+
+pySim-trace also understands the parameters passed to commands and how to decode them, for example
+of the AUTHENTICATE command within the USIM/ISIM/HPSIM application.
+
+
+Demo
+----
+
+To get an idea how pySim-trace usage looks like, you can watch the relevant part of the 11/2022
+SIMtrace2 tutorial whose `recording is freely accessible <https://media.ccc.de/v/osmodevcall-20221019-laforge-simtrace2-tutorial#t=2134>`_.
+
+
+Running pySim-trace
+-------------------
+
+Running pySim-trace requires you to specify the *source* of the to-be-decoded APDUs. There are several
+supported options, each with their own respective parameters (like a file name for PCAP decoding).
+
+See the detailed command line reference below for details.
+
+A typical execution of pySim-trace for doing live decodes of *GSMTAP (SIM APDU)* e.g. from SIMtrace2 or
+osmo-qcdiag would look like this:
+
+::
+
+ ./pySim-trace.py gsmtap-udp
+
+This binds to the default UDP port 4729 (GSMTAP) on localhost (127.0.0.1), and decodes any APDUs received
+there.
+
+
+
+pySim-trace command line reference
+----------------------------------
+
+.. argparse::
+ :module: pySim-trace
+ :func: option_parser
+ :prog: pySim-trace.py
+
+
+Constraints
+-----------
+
+* In order to properly track the current location in the filesystem tree and other state, it is
+ important that the trace you're decoding includes all of the communication with the SIM, ideally
+ from the very start (power up).
+
+* pySim-trace currently only supports ETSI UICC (USIM/ISIM/HPSIM) and doesn't yet support legacy GSM
+ SIM. This is not a fundamental technical constraint, it's just simply that nobody got around
+ developing and testing that part. Contributions are most welcome.
+
+