Suggested text updates on the "donate-to-osm" subpage

[dorotheakazazi]

Page: https://welcome.openstreetmap.org/about-osm-community/donate-to-osm/

The OSMF has updated its Corporate Membership program.

I suggest the following changes:

• "€500 for the Supporter level and go up to €20,000" to "€750 for the Supporter level and go up to €30,000"
• "Corporate members of Silver and higher levels" to "Corporate members of Bronze and higher levels"
• https://donate.openstreetmap.org/ to https://supporting.openstreetmap.org/donate/