[clang] [clang][docs] Update CommandLineUsage and UsersManual with some flags (PR #209519)

[Ehren Bendler via cfe-commits]

================
@@ -332,6 +332,27 @@ effect on formatting a simple conversion diagnostic, follow:
   ```
   t.c +3:11: warning: conversion specifies type 'char *' but the argument has type 'int'
   ```
+
+- **sarif**: Emit diagnostics as a [SARIF](https://docs.oasis-open.org/sarif/sarif/v2.1.0/sarif-v2.1.0.html) JSON
+  document. This is useful when diagnostics are consumed by tools, including AI
+  agents. SARIF diagnostics are written to standard error.
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ebendler wrote:

Sorry, got stuck on the doc formatting changes and missed it here.

https://github.com/llvm/llvm-project/pull/209519