docs: prominent input-format warning (this is a gene-ID model, not nucleotide)

README.md

@@ -7,6 +7,15 @@ tags:
 pipeline_tag: fill-mask
 ---
 
+> ⚠️ **Input format**: this model uses a Geneformer-style WordLevel
+> tokenizer whose vocabulary is **ENSEMBL gene IDs only** (e.g.
+> `ENSG00000000003`). Plain nucleotide strings (`AUGCAUGC...`) or
+> free text will NOT tokenize correctly — they collapse to one
+> `[UNK]` and the MLM head will return an ENSG-id at that mask
+> position by design. See the Example Output below for the correct
+> list-of-tokens calling convention.
+
+
 # molcrawl-rna-celltype-bert-medium
 
 ## Model Description