Clarify about evaluating the `comment` ”symbol” itself

[PEZ]

This issue on Calva BetterThanTomorrow/calva#1273 notes that you get an error when evaluating the comment word.

I think the solution is to try clarify that this is expected behaviour. Maybe somewhere here:

dram/drams/calva_getting_started/hello_repl.clj

Line 199 in f4266fd

;; == You Control what is Evaluated ==