Add events page

[maxrjones]

It would be helpful to create a page with information about upcoming and past Pangeo events

Upcoming events:

• https://discourse.pangeo.io/t/post-agu-pangeo-working-meeting-december-14-2024-in-washington-dc/4440
• https://discourse.pangeo.io/t/call-for-participation-in-pangeo-europe-at-egu2025/4473

Past events:

• https://discourse.pangeo.io/t/post-ams-pangeo-working-meeting-january-13-2023-in-denver-co/2831
• https://github.com/pangeo-data/pangeo/blob/master/docs/meetings/2019_european-pangeo-meeting.rst
• https://github.com/pangeo-data/pangeo/blob/master/docs/meetings/2019_summer-meeting.rst
  ... probably others