Mention migration to OLS4 on the homepage

[sneumann]

Hi,

Is your feature request related to a problem? Please describe. Over the past months, the OLS3 page mentioned the upcoming move to OLS4, with a link to test-drive OLS4. Now that the switch happened, software might encounter issues, (e.g., https://github.com/ISA-tools/OntoMaton/issues/39) Since people might've missed the months-long pre-notice, they come to https://www.ebi.ac.uk/ols/ (redirected to /ols4), and there is no news about the change.

Describe the solution you'd like The Report an Issue section could mention For details about the migration to the new OLS4 system in Nov. 2023 see ...

Yours, Steffen