Add firsts contribution instructions

Author: AbcSxyZ

README.md

@@ -7,6 +7,14 @@ See online : <https://open-models.github.io/open-calendar/>
 **The recommended use is to import the calendar into your personal calendar (Thunderbird, Google Calendar...) through the
 `calendar.ics` file : <https://raw.githubusercontent.com/Open-Models/open-calendar/refs/heads/main/calendar.ics>**
 
+## Contribute
+
+The most basic way to share your event on the calendar is through repository's
+[issues](https://github.com/Open-Models/open-calendar/issues).
+The event can then be integrated manually by a maintainer.
+
+If you have some programming skills, you can try your hand at improving this piece of code. Experimental project.
+
 ## Installation
 
 First, download the repository locally.

website/calendar.html

@@ -42,7 +42,9 @@ <h6><strong>Title:</strong> <span id="modalTitle"></span></h6>
             <img src="https://github.githubassets.com/images/modules/logos_page/GitHub-Mark.png"
                  alt="GitHub Logo" class="github-logo" style="width: 20px; height: 20px; vertical-align: middle;">
             View this project on GitHub
-        </a>
+        </a> 
+        |
+        Submit an event through <a href="https://github.com/Open-Models/open-calendar/issues">issues</a>.
     </footer>
 
     <!-- FullCalendar JS -->