new title for NHSN page

Author: nmdefries

docs/api/covidcast-signals/nhsn.md

@@ -4,7 +4,7 @@ parent: Data Sources and Signals
 grand_parent: Main Endpoint (COVIDcast)
 nav_order: 1
 ---
-# National Syndromic Surveillance Program Emergency Department Visits
+# National Healthcare Safety Network Respiratory Hospitalizations
 {: .no_toc}
 
 * **Source name:** `nhsn`