profiling: document the py-spy value for `profiling.type`

The feature was not visible otherwise.

mercurial/helptext/config.txt

@@ -2046,6 +2046,9 statistical text report generated from t
       Use a statistical profiler, statprof. This profiler is most
       useful for profiling commands that run for longer than about 0.1
       seconds.
+    ``py-spy``
+      use the py-spy profiler. A external py-spy executable must be available.
+      (Make sure to check `profiling.output` config to write the result.)
 
 ``format``
     Profiling format.  Specific to the ``ls`` instrumenting profiler.

tests/test-help.t

@@ -1605,7 +1605,7 Show nested definitions
 ("profiling.type"[break]"ls"[break]"stat"[break])
 
   $ hg help config.type | grep -E '^$'|wc -l
-  \s*3 (re)
+  \s*4 (re)
 
   $ hg help config.profiling.type.ls
           "profiling.type.ls"