Add CA2026 to rules missing documentation

Author: xtqqczze

src/Microsoft.CodeAnalysis.NetAnalyzers/src/RulesMissingDocumentation.md

@@ -6,3 +6,4 @@ CA1873 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-
 CA1874 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1874> | Use 'Regex.IsMatch' |
 CA1875 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1875> | Use 'Regex.Count' |
 CA2023 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2023> | Invalid braces in message template |
+CA2026 | <https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2026> | Prefer JsonElement.Parse over JsonDocument.Parse().RootElement |