Update index.md

Fix links, uses underscore not middlebar for file name

index.md

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 The objective of this site is to provide documentation to help muggles and aspiring wizards to better understand Grin. On purpose I specify "Grin" and not "mimblewimble" since I want to be as practically orietented and very explicit in this documentation. I hope it will help you on your journey down the Grin rabbit hole. Writing this documentation  certainly helped me to acchieve greater clarity.  
 
 ## Table of contents
-1) [Grin for muggles and aspiring  wizards](https://anynomouss.github.io/grin-for-muggles/grin-for-muggles-and-aspiring-wizards.html) <br>
-2) [Grin in data](https://anynomouss.github.io/grin-for-muggles/grin-in-data.html) <br>
+1) [Grin for muggles and aspiring  wizards](https://anynomouss.github.io/grin-for-muggles/grin_for_muggles_and_aspiring_wizards.html) <br>
+2) [Grin in data](https://anynomouss.github.io/grin-for-muggles/grin_in_data.html) <br>
 3) Grin transaction relay system concept <br>