[STYLE] Minor markdown style tweak

Changes in file docs/INSTALL.md:
 * markdown style tweak

Author: reactive-firewall

docs/INSTALL.md

@@ -67,11 +67,10 @@ python3 -m multicast --version
 pip install -e "git+https://github.com/reactive-firewall/multicast.git#egg=multicast"
 ```
 
----
+***
 
 If all went well, `multicast` is now installed and working :tada:
 
-
 ***
 
 #### Copyright (c) 2021-2025, Mr. Walls