I am no expert on Qatari labour law - however usually certain entitlements are implied into an employment contract by operation of law (a fancy way of saying because the law says so) - i.e the labour law states that certain employees are entitled to a certain amount of sick and annual leave (however employers and employees can contract for greater benefits then the minimum). So in short if your contract is silent the minimum applies.

I am quite sure this is the case in relation to these two benefits (sick and annual L) but I am unsure as to how much the entitlement is.

However this being said, you have to look at more importantly at wheather the offer in and of its self is worthwhile.

Cheers