Add data structures to topic list

We have a number of exercises that are about data structures, but the topic was missing.
exercism · Aug 24, 2019 · 8d22308 · 8d22308
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commit 8d22308
Showing 1 changed file with 1 addition and 0 deletions.
diff --git a/TOPICS.txt b/TOPICS.txt
@@ -50,6 +50,7 @@ algorithms
 bitwise_operations
 concurrency
 cryptography
+data_structures
 domain_specific_languages
 files
 filtering