add opc to readme
@@ -596,6 +596,7 @@ Please take a quick gander at the [contribution guidelines](https://github.com/a
* [go-decent-copy](https://github.com/hugocarreira/go-decent-copy) - Copy files for humans.
* [go-gtfs](https://github.com/artonge/go-gtfs) - Load gtfs files in go.
* [notify](https://github.com/rjeczalik/notify) - File system event notification library with simple API, similar to os/signal.
+* [opc](https://github.com/qmuntal/opc) - Load Open Packaging Conventions (OPC) files for Go.
* [pdfcpu](https://github.com/hhrutter/pdfcpu) - PDF processor.
* [skywalker](https://github.com/dixonwille/skywalker) - Package to allow one to concurrently go through a filesystem with ease.
* [tarfs](https://github.com/posener/tarfs) - Implementation of the [`FileSystem` interface](https://godoc.org/github.com/kr/fs#FileSystem) for tar files.
