Template for newsletter inputs (#424)

* template-addition

* fix formatting

Author: ramyaragupathy

.github/newsletter.md

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+Gathering updates for the MMM edition of the MapLibre newsletter! If you have project updates, community event announcements, or other highlights you’d like to share, please comment below.
+
+🕕 Submission Deadline: DD-MMM XX UTC
+🎫 Previous issue: https://github.com/maplibre/maplibre.github.io/issues/xxx
+🗒 Previous newsletters: https://maplibre.org/categories/newsletter/
+
+## What to Submit
+
+- Project updates (MapLibre GL JS, Native, plugins, etc.)
+- Community events, talks, or meetups
+- New features, demos, or documentation updates
+- We also invite submissions for Community Spotlights, that features projects built with MapLibre. To be featured:
+  - Your project must be open-source, or have a significant open-source component
+  - Projects that are non-commercial, non-profit-oriented or created for the public good will be prioritized.
+  - Please include a short description and a link (demo, repo, or blog post)
+  - Screenshots or gifs are a plus!
+  - _Please note we aim to highlight work that aligns with MapLibre’s community values rather than promotional or commercial content_