pySim-shell: Add settable parameter on JSON pretty-printing

Change-Id: Ic095c96733de2b0f359bfe067cd719d38712faff
diff --git a/docs/shell.rst b/docs/shell.rst
index 314f633..ddb21d5 100644
--- a/docs/shell.rst
+++ b/docs/shell.rst
@@ -208,6 +208,14 @@
 
 If disabled, pySim will always write irrespective of the current/new value.
 
+json_pretty_print
+~~~~~~~~~~~~~~~~~
+
+This parameter determines if generated JSON output should (by default) be pretty-printed (multi-line
+output with indent level of 4 spaces) or not.
+
+The default value of this parameter is 'true'.
+
 debug
 ~~~~~