shell: Add 'apdu_trace' settable parameter for hex-dumping APDUs

Change-Id: I0c957c0b86473413f31e4bd8bc4e633fc1470222
diff --git a/docs/shell.rst b/docs/shell.rst
index 06e7f42..854944c 100644
--- a/docs/shell.rst
+++ b/docs/shell.rst
@@ -328,6 +328,11 @@
 
 If enabled, full python back-traces will be displayed in case of exceptions
 
+apdu_trace
+~~~~~~~~~~
+
+Boolean variable that determines if a hex-dump of the command + response APDU shall be printed.
+
 numeric_path
 ~~~~~~~~~~~~