ts_31_102: Add decoder/encoder for DF.5GS/EF.Routing_Indicator

This file is rather important for 5G SA operation, so we should have
a proper encoder/decoder in place.

Change-Id: I1b37fdfc2807976880b2cafb61951f08eebeb344
diff --git a/docs/suci-tutorial.rst b/docs/suci-tutorial.rst
index 00c060f..fc6e911 100644
--- a/docs/suci-tutorial.rst
+++ b/docs/suci-tutorial.rst
@@ -132,10 +132,8 @@
 
 ::
 
-   pySIM-shell (MF/ADF.USIM/DF.5GS/EF.Routing_Indicator)> update_binary 0071ffff
+   pySIM-shell (MF/ADF.USIM/DF.5GS/EF.Routing_Indicator)> update_binary 17ffffff
 
-(the encoding might be different, see `this
-comment <https://gist.github.com/mrlnc/01d6300f1904f154d969ff205136b753?permalink_comment_id=4050795#gistcomment-4050795>`__)
 You can also set the routing indicator to **0x0**, which is *valid* and
 means “routing indicator not specified”, leaving it to the modem.