added update-registry scripts

companion/win/chrome/update-registry.bat

@@ -0,0 +1,2 @@
+@echo off
+reg add "HKLM\Google\Chrome\NativeMessagingHosts\singlefile_companion" /ve /t REG_SZ /d "%~dp0\singlefile_companion.json" /f

companion/win/firefox/update-registry.bat

@@ -0,0 +1,3 @@
+@echo off
+reg add "HKCU\Software\Mozilla\NativeMessagingHosts\singlefile_companion" /ve /t REG_SZ /d "%~dp0\singlefile_companion.json" /f
+reg add "HKLM\Software\Mozilla\NativeMessagingHosts\singlefile_companion" /ve /t REG_SZ /d "%~dp0\singlefile_companion.json" /f