Fix punctuation in overview.md (#339)

Added a semicolon for clarity in the Concepts section.

Signed-off-by: Luke Zhan <[email protected]>

Author: 1spyral

website/versioned_docs/version-3.21.0/concepts/overview.md

@@ -6,7 +6,7 @@ sidebar_label: Overview
 
 ---
 
-The Concepts section contains Definitions, Design principles, Terminology and Working technical theory. This section will not have the actual usage instructions or guides those will be made available in the [User Guides](../user-guides/overview.md) section.
+The Concepts section contains Definitions, Design principles, Terminology and Working technical theory. This section will not have the actual usage instructions or guides; those will be made available in the [User Guides](../user-guides/overview.md) section.
 
 ### [Chaos Infrastructure](infrastructure.md)