Update crontrigger.md

[rpringadi]

So cron expressions can be as simple as this: * * * * ? *

Value number 5 is for Month.
In the table right above it, we don't see question mark as an "Allowed Special Characters"

Month	YES	1-12 or JAN-DEC	, - * /

So either we change this sentence, or change the table value.

[jhouserizer]

Hello! Thank you very much for your contribution and interest in helping improve the Quartz community.

After a period of dormancy, the Quartz project is back under steady maintenance by multiple volunteers, who are working to once again handle contributions such as yours.

We notice that your contribution was made without use of the DCO feature (the sign-off feature on commits via the -s option). Can you please update your PR with commits that use the -s option, agreeing to assign copyright ownership and other terms as described at the contributor agreement referenced here: https://github.com/quartz-scheduler/contributing/blob/main/CONTRIBUTING.md

You can easily add signoff to your previous commits by running (on your PR branch):

git commit --amend --signoff --no-edit 
git push -f

Or (for multiple commits):

# change 5 to the number of commits
git rebase HEAD~5 --signoff
git push -f

[knutsenm]

In the table right above it, we don't see question mark as an "Allowed Special Characters"

Can you please update your PR with commits that use the -s option

Please, somebody fix the docs.