Update README.md

[Sheru16]

added Composio

[Pratiyush]

⚠️ This repository is no longer actively maintained.

Many entries are outdated (Heroku, PlanetScale, SendGrid, Fauna — all removed free tiers). For an actively maintained alternative with 323 verified entries in structured tables,
see free-stack.

Step 3: Open PR from your fork to their repo
! open "https://github.com/jixserver/free-for-dev/compare/master...Pratiyush:master?expand=1"

PR Title: Add notice about outdated entries + link to maintained alternative

PR Body:
Many entries in this list are outdated — services like Heroku, PlanetScale,
SendGrid, Fauna, and ElephantSQL have removed their free tiers or shut down.

This PR adds a notice at the top pointing to an actively maintained alternative
(free-stack) with 323 verified entries across 27 categories in structured tables.

Happy to help maintain this repo instead if you'd prefer to keep it alive.