I would write one and keep it short. Nobody wants to read a huge block of text. For startups, I've always kept it informal and sent it as an email.
Hi Team,
I'm a software engineer in [LOCATION] looking for new opportunities. I have experience with your stack and would love to hear more about the company and openings.
You can see more from me here:
[WEBSITE/GITHUB LINK]
Please have a glance at my resume and see if my skills and experience could be useful.
Thanks,
[FIRST LAST NAME]