chore[tool]: mention that output format is comma separated (#4467)

because the -p flag is multiple (e.g. `-p path1 -p path2`) whereas
output format is comma separated, this can lead to confusion for
users. add a note to the help text.

vyper/cli/vyper_compile.py

@@ -17,7 +17,7 @@
 from vyper.typing import ContractPath, OutputFormats
 from vyper.utils import uniq
 
-format_options_help = """Format to print, one or more of:
+format_options_help = """Format to print, one or more of (comma-separated):
 bytecode (default) - Deployable bytecode
 bytecode_runtime   - Bytecode at runtime
 blueprint_bytecode - Deployment bytecode for an ERC-5202 compatible blueprint