Add a note to the README about SQL timings absence when generating fl…

…amegraphs (#507)

README.md

@@ -175,6 +175,9 @@ To store flamegraph data for later viewing, append the `?pp=async-flamegraph` pa
 Flamegraph data for this request, and all subsequent requests made by this page (based on the `REFERER` header) will be stored.
 'flamegraph' links will appear for these requests in the MiniProfiler UI.
 
+Note: Mini Profiler will not record SQL timings for a request if it asks for a flamegraph. The rationale behind this is to keep
+Mini Profiler's methods that are responsible for generating the timings data out of the flamegraph.
+
 ### Memory Profiling
 
 Memory allocations can be measured (using the [memory_profiler](https://github.com/SamSaffron/memory_profiler) gem)