add link in doc

README.md

@@ -15,7 +15,7 @@ Provides [empirical cumulative distribution functions (CDFs)](https://en.wikiped
 It is useful especially for examining the
 tail of the CDF obtained from streaming a large number of data, more than can be stored in memory.
 For this purpose, you specify a lower cutoff; data points below this value will be silently rejected, but the
-resulting CDF will still be properly normalized. This ability to process and filter data online
+resulting CDF will still be properly normalized. This ability to process and filter data [online](https://en.wikipedia.org/wiki/Online_algorithm)
 is absent in `StatsBase.ecdf`.
 
 ```julia