[rtsan][NFC] Add documentation link to Function Effects (llvm#113979)

Author: cjappl

clang/docs/RealtimeSanitizer.rst

@@ -11,11 +11,16 @@ RealtimeSanitizer (a.k.a. RTSan) is a real-time safety testing tool for C and C+
 projects. RTSan can be used to detect real-time violations, i.e. calls to methods
 that are not safe for use in functions with deterministic run time requirements.
 RTSan considers any function marked with the ``[[clang::nonblocking]]`` attribute
-to be a real-time function. If RTSan detects a call to ``malloc``, ``free``,
-``pthread_mutex_lock``, or anything else that could have a non-deterministic
-execution time in a function marked ``[[clang::nonblocking]]``
+to be a real-time function. At run-time, if RTSan detects a call to ``malloc``, 
+``free``, ``pthread_mutex_lock``, or anything else that could have a 
+non-deterministic execution time in a function marked ``[[clang::nonblocking]]``
 RTSan raises an error.
 
+RTSan performs its analysis at run-time but shares the ``[[clang::nonblocking]]`` 
+attribute with the :doc:`FunctionEffectAnalysis` system, which operates at 
+compile-time to detect potential real-time safety violations. For comprehensive 
+detection of real-time safety issues, it is recommended to use both systems together.
+
 The runtime slowdown introduced by RealtimeSanitizer is negligible.
 
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