Add global sponsors

pelicanconf.py

+from datetime import date
+
+SPONSORS = [
+    ("SpeedPartner", "/images/sponsors/speedpartner.png", "https://www.speedpartner.de", date(2038, 12, 31)),
+    ("Informatik aktuell", "/images/sponsors/informatik_aktuell.png", "https://www.informatik-aktuell.de/", date(2021, 12, 31)),
+    ("Python Software-Verband e.V.", "/images/sponsors/pysv.png", "https://www.python-verband.org", date(2021, 7, 31)),
+    ("Proxmox Server Solutions GmbH", "/images/sponsors/proxmox.png", "https://proxmox.com", date(2022, 4, 30)),
+    ]