Added missing periods for consistency and correctness (#2250)

Added missing periods in various parts of the text to ensure consistency and correctness in writing style. This revision maintains uniform formatting throughout the document, improves readability, and aligns the punctuation with the rest of the content for a more polished and structured appearance.

Author: shaymolcho

CppCoreGuidelines.md

@@ -21,9 +21,9 @@ The list of contributors is [here](#SS-ack).
 Problems:
 
 * The sets of rules have not been completely checked for completeness, consistency, or enforceability.
-* Triple question marks (???) mark known missing information
+* Triple question marks (???) mark known missing information.
 * Update reference sections; many pre-C++11 sources are too old.
-* For a more-or-less up-to-date to-do list see: [To-do: Unclassified proto-rules](#S-unclassified)
+* For a more-or-less up-to-date to-do list see: [To-do: Unclassified proto-rules](#S-unclassified).
 
 You can [read an explanation of the scope and structure of this Guide](#S-abstract) or just jump straight in: