Add supported browsers to doc/INSTALL (#34978).

Patch by Go MAEDA. 


git-svn-id: http://svn.redmine.org/redmine/trunk@21478 e93f8b46-1217-0410-a6f0-8f06a7374b81

doc/INSTALL

@@ -21,6 +21,9 @@ Optional:
   available in PATH)
 * ImageMagick (to enable Gantt export to png images)
 
+Supported browsers:
+The current version of Firefox, Safari, Chrome, and Microsoft Edge.
+
 == Installation
 
 1. Uncompress the program archive