docs: improve README examples of stats/base/dists/signrank namespace

lib/node_modules/@stdlib/stats/base/dists/signrank/README.md

@@ -34,6 +34,13 @@ var signrank = require( '@stdlib/stats/base/dists/signrank' );
 
 Distribution of the Wilcoxon signed rank test statistic.
 
+The Wilcoxon distribution is a discrete, bell-shaped, non-negative distribution, which describes the distribution of the U-statistic in the Mann-Whitney-Wilcoxon Rank-Sum test when comparing two unpaired samples drawn from the same arbitrary distribution. The rank-sum test is perhaps the most commonly used non-parametric significance test in statistics to detect when one distribution is stochastically greater (or not-equal) to another without making assumption that the underlying distributions are normally distributed. 
+
+Reference: <br>
+- [Wikipedia](https://en.wikipedia.org/wiki/Wilcoxon_signed-rank_test) <br>
+- [Analytica](https://docs.analytica.com/index.php/Wilcoxon_Distribution)
+
+
 ```javascript
 var dist = signrank;
 // returns {...}
@@ -63,15 +70,107 @@ The namespace contains the following distribution functions:
 
 <!-- TODO: better examples -->
 
-<!-- eslint no-undef: "error" -->
 
+   <!-- eslint no-undef: "error" -->
+### Object Keys
 ```javascript
 var objectKeys = require( '@stdlib/utils/keys' );
 var signrank = require( '@stdlib/stats/base/dists/signrank' );
 
 console.log( objectKeys( signrank ) );
 ```
 
+### Cumulative Distribution Function (CDF)
+```javascript
+var cdf = require( '@stdlib/stats/base/dists/signrank/cdf' );
+```
+#### cdf( x, n )
+
+Evaluates the [cumulative distribution function][cdf] of the Wilcoxon signed rank test statistic with `n` observations.
+
+```javascript
+var y = cdf( 7.0, 9 );
+// returns ~0.037
+
+y = cdf( 7.0, 6 );
+// returns ~0.281
+
+y = cdf( -1.0, 40 );
+// returns 0.0
+```
+
+#### cdf.factory( n )
+
+Returns a function for evaluating the [cumulative distribution function][cdf] of the Wilcoxon signed rank test statistic with `n` observations.
+
+```javascript
+var mycdf = cdf.factory( 8 );
+var y = mycdf( 3.9 );
+// returns ~0.027
+
+y = mycdf( 17.0 );
+// returns ~0.473
+```
+
+### Probability Distribution Function (PDF)
+```javascript
+var pdf = require( '@stdlib/stats/base/dists/signrank/pdf' );
+```
+#### pdf( x, n )
+Evaluates the [probability density function][pdf] of the Wilcoxon signed rank test statistic with `n` observations.
+```javascript
+var y = pdf( 7.0, 9 );
+// returns ~0.0098
+
+y = pdf( 7.0, 6 );
+// returns ~0.063
+
+y = pdf( -1.0, 40 );
+// returns 0.0
+```
+
+#### pdf.factory( n )
+Returns a function for evaluating the [probability density function][pdf] of the Wilcoxon signed rank test statistic with `n` observations.
+```javascript
+var mypdf = pdf.factory( 8 );
+var y = mypdf( 4.0 );
+// returns ~0.008
+
+y = mypdf( 17.0 );
+// returns ~0.051
+```
+
+### Quantile Function
+```javascript
+var quantile = require( '@stdlib/stats/base/dists/signrank/quantile' );
+```
+#### quantile( p, n )
+
+Evaluates the [quantile function][quantile-function] for the Wilcoxon signed rank test statistic with `n` observations.
+
+```javascript
+var y = quantile( 0.8, 5 );
+// returns 11
+
+y = quantile( 0.5, 3 );
+// returns 3
+```
+
+#### quantile.factory( n )
+
+Returns a function for evaluating the [quantile function][quantile-function] of the Wilcoxon signed rank test statistic with `n` observations.
+
+```javascript
+var myQuantile = quantile.factory( 8 );
+
+var y = myQuantile( 0.4 );
+// returns 16
+
+y = myQuantile( 1.0 );
+// returns 36
+```
+
+
 </section>
 
 <!-- /.examples -->