Add PSF & replace Pyvec logo with PyCon CZ one

Author: clytaemnestra

src/content/sponsors/psf/index.md

@@ -0,0 +1,10 @@
+---
+name: "Python Software Foundation"
+url: "https://pycon.at"
+location: "US"
+industry: "Technology & Non-Profit"
+description:
+  "The Python Software Foundation is an organization devoted to advancing open source technology related to the Python programming language."
+tier: Gold
+logo_padding: 10px 0
+---