Standardize MD unordered bullet symbol in README.md

The existing convention is to use a hyphen for unordered lists. In a previous PR I probably habitually used an asterisk.

Swap two references bullet points from asterisk to hyphen.

Author: mjbear

README.md

@@ -264,5 +264,5 @@ wsl -l -v
 
 # Reference Material
 
-* https://learn.microsoft.com/en-us/windows/wsl/use-custom-distro#export-the-tar-from-a-container
-* https://learn.microsoft.com/en-us/windows/wsl/build-custom-distro
+- https://learn.microsoft.com/en-us/windows/wsl/use-custom-distro#export-the-tar-from-a-container
+- https://learn.microsoft.com/en-us/windows/wsl/build-custom-distro