Add Isogram topics

Referencing #788

conditionals: finding if a char is repeated
loops: looping through a string's characters
parsing: parsing a string for repeated characters
strings: self-explanatory :)

config.json

@@ -232,7 +232,7 @@
         "loops",
         "strings",
         "algorithms",
-        "parsing",
+        "parsing"
       ],
       "unlocked_by": "hello-world",
       "uuid": "c3e89c7c-3a8a-4ddc-b653-9b0ff9e1d7d8"