close #4451 (#17627)

doc/estp.rst

@@ -21,6 +21,14 @@ You can in fact look at `nimprof`'s source code to see how to implement
 your own profiler.
 
 The setting `--profiler:on` defines the conditional symbol `profiler`.
+You can use `when compileOption("profiler")` to make the switch seamless.
+If `profiler` is `off`, your program runs normally. Otherwise your program
+is profiled.
+
+```nim
+when compileOption("profiler"):
+  import nimprof
+```
 
 After your program has finished the profiler will create a
 file `profile_results.txt` containing the profiling results.

lib/pure/nimprof.nim

@@ -9,7 +9,8 @@
 
 ## Profiling support for Nim. This is an embedded profiler that requires
 ## `--profiler:on`. You only need to import this module to get a profiling
-## report at program exit.
+## report at program exit. See `Embedded Stack Trace Profiler <estp.html>`_
+## for usage.
 
 when not defined(profiler) and not defined(memProfiler):
   {.error: "Profiling support is turned off! Enable profiling by passing `--profiler:on --stackTrace:on` to the compiler (see the Nim Compiler User Guide for more options).".}