docs: Fix Discord server link formatting

Author: ryanmccann1024

README.md

@@ -6,7 +6,7 @@
 
 **Documentation: [https://sdnnetsim.github.io/FUSION/](https://sdnnetsim.github.io/FUSION/)**
 
-**Discord Server: [https://discord.gg/3M4gX7ua)**
+**Discord Server: [https://discord.gg/3M4gX7ua](https://discord.gg/3M4gX7ua)**
 
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