update docs

Author: CyrusNajmabadi

src/Features/RulesMissingDocumentation.md

@@ -4,6 +4,7 @@ Rule ID | Missing Help Link | Title |
 --------|-------------------|-------|
 IDE0005_gen |  | Imports statement is unnecessary. |
 IDE0043 |  | Invalid format string |
+IDE0121 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0121> | Simplify LINQ expression |
 IDE0290 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0290> | Use primary constructor |
 IDE0300 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0300> | Simplify collection initialization |
 IDE0301 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0301> | Simplify collection initialization |