Standardize Walkthrough footer

Author: syreal17

example-problems/forensics-disk/README.md

@@ -131,4 +131,5 @@ downloadable artifacts, with base64 encoding probably being the preferred
 method. Salting a flag can help a base64 blob be nearly impossible to grep for.
 
 [Next problem](/example-problems/web-css)
+
 [Return to the index](/example-problems#example-problems)

example-problems/sanity-static-flag/README.md

@@ -156,3 +156,5 @@ categories and more!
 
 Check out [forensics grep](/example-problems/forensics-grep) to learn how to
 create and use dynamic flags!
+
+[Return to index](/example-problems#example-problems)

example-problems/web-css/README.md

@@ -72,4 +72,5 @@ order to hide the flag in one of these files. We used Python to configure this
 container which leads to a cleaner implementation.
 
 [Next problem](/example-problems/reversing-python)
+
 [Return to the index](/example-problems#example-problems)