Remove the starting '*' from block comments

godoc doesn't recognise the C-style block comments convention of prefixing each line with a '*', so these need to be removed or they show up in the godoc output.
Add a file to home the package documentation
Clarify the intent of the pivot selection strategies

When seen in the context of godoc output these functions are a little confusing. Clarified the doc comments to show they relate to quick sort and should be used with QuickSortWithPivotChoice.