remove needless "is" from selection string

[richardjgowers]

hey @sef43 this is very cool. One thing I spotted was that the example selection looks a little odd. The syntax is just "name X [Y Z]" for select all atoms with name(s) X (or Y or Z). The current example is selecting atoms called is or C, which will work but isn't what you intended

[sef43]

Thank you for pointing this out!