Add README to draw2dpdf

draw2dpdf/README.md

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+draw2d pdf
+==========
+
+Package draw2dpdf provides a graphic context that can draw vector graphics and text on pdf file with the [gofpdf](https://github.com/jung-kurt/gofpdf) package.
+
+Quick Start
+-----------
+
+The following Go code generates a simple drawing and saves it to a pdf document:
+```go
+// Initialize the graphic context on an RGBA image
+dest := draw2dpdf.NewPdf("L", "mm", "A4")
+gc := draw2d.NewGraphicContext(dest)
+
+// Set some properties
+gc.SetFillColor(color.RGBA{0x44, 0xff, 0x44, 0xff})
+gc.SetStrokeColor(color.RGBA{0x44, 0x44, 0x44, 0xff})
+gc.SetLineWidth(5)
+
+// Draw a closed shape
+gc.MoveTo(10, 10) // should always be called first for a new path
+gc.LineTo(100, 50)
+gc.QuadCurveTo(100, 10, 10, 10)
+gc.Close()
+gc.FillStroke()
+
+// Save to file
+draw2dpdf.SaveToPdfFile("hello.pdf", dest)
+```
+
+There are more examples here: https://github.com/llgcode/draw2d/tree/master/samples
+
+Alternative backends
+--------------------
+
+- Drawing on images is provided by the draw2d package.
+- Drawing on opengl is provided by the draw2dgl package.
+
+Acknowledgments
+---------------
+
+The pdf backend uses https://github.com/jung-kurt/gofpdf