Update ref.md

docs/src/en/ref.md

@@ -3,6 +3,12 @@
 Fetch FTPs and their respective metadata (or use flag `ftp` to only return the links) for reference genomes and annotations from [Ensembl](https://www.ensembl.org/) by species.  
 Return format: dictionary/JSON.
 
+```diff
+! While Ensembl is in the process of updating its database to a new release, you might receive a 404 error.
+```
+> If this is the case, specify an earlier Ensembl version using the `release` argument.  
+> Example: `gget ref -r 110 human` (Python: `gget.ref("human", release=110)`)
+
 **Positional argument**  
 `species`  
 Species for which the FTPs will be fetched in the format genus_species, e.g. homo_sapiens.