docs: update changelog

Author: sgratzl

content/covidcast/release-log/headless/v2.0.0.md

@@ -1,12 +1,14 @@
 ---
 title: v2.0.0
-date: 2021-03-05
+date: 2021-03-19
 ---
 
 ### Signal Changes
 
-- Replaced "Vaccine Acceptance" with signal including both already received the vaccine and definitely or probably choose to get vaccinated.
-
+- Replace "Vaccine Acceptance" with signal including both already received the vaccine and definitely or probably choose to get vaccinated.
+- Change "People Wearing Masks" signal to its latest revision
+- Add "COVID Symptom Searches on Google" signal to map and COVIDcast 2.0
+- Change survey result signals to their latest revisions with the option to explore old revisions
 
 ### New Features