Update README.md

Downloading some pre-built `.db` files with curl doesn't work. Downloading the `.db.gz` does.

README.md

@@ -20,7 +20,7 @@ sqlite> SELECT * FROM rdfs_label_statement WHERE value LIKE 'Abnormality of %';
 |HP:0000032|HP:0000032|rdfs:label||Abnormality of male external genitalia|xsd:string||
 
 
-Ready-made SQLite3 builds can also be downloaded for any ontology in [OBO](http://obofoundry.org), using URLs such as https://s3.amazonaws.com/bbop-sqlite/hp.db
+Ready-made SQLite3 builds can also be downloaded for any ontology in [OBO](http://obofoundry.org), using URLs such as https://s3.amazonaws.com/bbop-sqlite/hp.db.gz
 
 [relation-graph](https://github.com/balhoff/relation-graph/) is used to pre-generate tables of [entailed edges](https://incatools.github.io/semantic-sql/EntailedEdge/). For example,
 all is-a and part-of ancestors of [finger](http://purl.obolibrary.org/obo/UBERON_0002389) in Uberon:
@@ -73,7 +73,7 @@ semsql download obi -o obi.db
 
 Or simply download using URL of the form:
 
-- https://s3.amazonaws.com/bbop-sqlite/hp.db
+- https://s3.amazonaws.com/bbop-sqlite/hp.db.gz
 
 ## Attaching databases