ADD documentaton for runstest

From current `R CMD check`

```
  generic 'plotRunstest' and siglist 'FLQuants,FLQuants'
  generic 'runstest' and siglist 'a4aFitSA,FLIndices'
  generic 'runstest' and siglist 'FLQuants,FLQuants'
  generic 'runstest' and siglist 'FLQuants,missing'
```