Please update the README

[jchristn]

Describe the bug
Examples of use of ObjectExtractor indicate a class vs a static.

To Reproduce
Attempt to build with this code:

using (PdfDocument document = PdfDocument.Open("doc.pdf", new ParsingOptions() { ClipPaths = true }))
{
	ObjectExtractor oe = new ObjectExtractor(document);
	PageArea page = oe.Extract(1);

	IExtractionAlgorithm ea = new SpreadsheetExtractionAlgorithm();
	List<Table> tables = ea.Extract(page);
	var table = tables[0];
	var rows = table.Rows;
}

Expected behavior
Code will compile.

Screenshots
From the source:

    public static class ObjectExtractor
    {
        private const int rounding = 6;

        private const float RULING_MINIMUM_LENGTH = 0.01f;

Additional context
Thanks for this great library!