Show supervision description for DAI d

[danyill]

Typically we show A > B

LN[lnClass="LGOS/LSVS" desc="A"] > DOI[name="St][desc="B"]

We will also now show A > B for this case:

<LN lnClass="LGOS" inst="2" lnType="Dummy.LGOS" desc="A">
	<Private type="OpenSCD.create"/>
	<DOI name="St">
		<DAI name="d">
			<Val>B</Val>
		</DAI>
	</DOI>
	<DOI name="GoCBRef">
		<DAI name="setSrcRef">
			<Val></Val>
		</DAI>
	</DOI>
</LN>

This is somewhat debatable as it requires a DOI for St which perhaps not all tools do.
Previously I used the description on the DOI[name="GoCBRef"] but the description on St is more likely to be used e.g. in SCADA/MMS and so having it in just this place prevents duplication.

I don't have a better idea, so that's what we'll do for now.