Cannot add conditions in Nexus

[arnaudlimbourg]

When the switch name has spaces it is not possible to add conditions to make the switch selective. When adding underscores it works properly though.

I have not investigated the nexus code base but I figured updating the documentation made sense.

[adamchainz]

Fixed using spaces in Switch keys on the YPlan fork in YPlan/gargoyle#38 , thanks for the report.