Dear Respected Hiring Manager,
I'm very interested in your job posting for a writer. In my position at my current company, I wrote feature articles for the website, managed content, and wrote a weekly email newsletter to my staff.
Examples of documentation, and more of my writing are available in my portfolio. In addition to that, I can assimilate new ideas efficiently and to grasp new concepts quickly. I look forward to hearing from you and thank you for your consideration.