Write articles about issues, policies and processes that are relevant. and need to be communicated to the staff in YOUR company.
Staff often need reminding about what they need to do in certain situations, such as taking leave, attendance, travel for work, training etc.
You could write about upcoming holidays and how the company will observe them, e.g. things like Diwali celebrations (which I know was this week, but just using as an example), or maybe some quick paras to introduce members of the HR team to staff. You just need to think logically about this.
The other thing you should think long and hard about is whether such a publication is necessary. What is the reason for producing this newsletter? What do you hope to gain from it? Will staff be interested? I am willing to bet they won't. You may find your time would be more productively spent in engaging with the staff face to face and dealing with their problems quickly and efficiently. That will win you far more friends than a impersonal newsletter.