createThread command not accurate in userguide

[nus-pe-script]

Wrong command description in user guide. Correct command description only found after entering wrong command in app
Also, unable to add question mark. Validation regex needs to be updated.

Steps to reproduce the behavior:

1. type createThread tTitle/About exams? cContent/Wow your app is so complicated

Expected behavior
Created thread

Screenshots

Additional context
NIL

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Reported by: @driedmelon
Severity: Medium

_{[original: nusCS2113-AY1819S1/pe-1#56]}