Improve background in README

README.md

@@ -23,11 +23,15 @@ Open `flamegraph.html` in a browser of your choice.
 [Flamegraphs](http://www.brendangregg.com/flamegraphs.html) were invented by
 Brendan Gregg to visualize CPU consumption of profiled code-paths of software.
 They are useful visualization tools in many types of performance
-investigations.
-
-Luca Canali has previously shown the benefits of using flamegraph
-visualizations of Oracle query plans for debugging slow database queries.
-Pg_flame is in extension of that work for Postgres.
+investigations. Luca Canali has previously shown the benefits of using
+[flamegraph visualizations of Oracle database
+profiles](https://externaltable.blogspot.com/2014/05/flame-graphs-for-oracle.html)
+for debugging slow database queries.
+
+Pg_flame is in extension of that work for Postgres query plans. Instead of
+being used to graph CPU time of internal Postgres functions, it generates a
+visual hierarchy to query plans. This visualization identifies the relative
+time of each part of a query plan, helping to direct optimization efforts.
 
 This tool relies on the
 [`d3-flame-graph`](https://github.com/spiermar/d3-flame-graph) plugin to