Add a little bit more description about profiling

As from the original article, we cannot learn what profiling is.

README.md

@@ -894,7 +894,7 @@ SQL tuning is a broad topic and many [books](https://www.amazon.com/s/ref=nb_sb_
 It's important to **benchmark** and **profile** to simulate and uncover bottlenecks.
 
 * **Benchmark** - Simulate high-load situations with tools such as [ab](http://httpd.apache.org/docs/2.2/programs/ab.html).
-* **Profile** - Enable tools such as the [slow query log](http://dev.mysql.com/doc/refman/5.7/en/slow-query-log.html) to help track performance issues.
+* **Profile** - Enable tools such as the [slow query log](http://dev.mysql.com/doc/refman/5.7/en/slow-query-log.html) to help measure the resource usage, tracking performance issues.
 
 Benchmarking and profiling might point you to the following optimizations.