doc: Update Notice emoji (#7424)

Just a simple update on the emoji so that it catch people attention as I
see many open issues about terminal not running on Windows Server 2016.

README.md

@@ -17,7 +17,7 @@ Related repositories include:
 
 ## Installing and running Windows Terminal
 
-> 👉 Note: Windows Terminal requires Windows 10 1903 (build 18362) or later
+> 🔴 Note: Windows Terminal requires Windows 10 1903 (build 18362) or later
 
 ### Microsoft Store [Recommended]
 
@@ -31,7 +31,7 @@ This is our preferred method.
 
 For users who are unable to install Terminal from the Microsoft Store, Terminal builds can be manually downloaded from this repository's [Releases page](https://github.com/microsoft/terminal/releases).
 
-> ⚠ Note: If you install Terminal manually:
+> 🔴 Note: If you install Terminal manually:
 >
 > * Be sure to install the [Desktop Bridge VC++ v14 Redistributable Package](https://www.microsoft.com/en-us/download/details.aspx?id=53175) otherwise Terminal may not install and/or run and may crash at startup
 > * Terminal will not auto-update when new builds are released so you will need to regularly install the latest Terminal release to receive all the latest fixes and improvements!