update doc

howto_generate_database.md

@@ -73,6 +73,7 @@ not planning to backup, or transfer this file, you can skip the next step, but
 the time used in the next step is very small, and this is not a good idea in
 general case.
 
+We don't need SOMEWHERE/srtm anymore. You can remove it.
 
 Converting elevation db
 -----------------------
@@ -95,7 +96,7 @@ Keep it
 Keep this elevation database. It is not needed to recreate it when the pbf is
 updated. Except the case when new area is added to the pbf which are not in the
 elevation database, but in this case, you will know it, the routing db (next
-part) creation will fail, with a explanation.
+part) creation will fail, with a explanation (maybe).
 
 
 Testing the elevation database