README: add discord link

README.md

@@ -1,6 +1,7 @@
 # giu
 
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+<iframe src="https://discord.com/widget?id=1306199225616306248&theme=dark" width="350" height="500" allowtransparency="true" frameborder="0" sandbox="allow-popups allow-popups-to-escape-sandbox allow-same-origin allow-scripts"></iframe>
 [![Go Report Card](https://goreportcard.com/badge/github.com/AllenDang/giu)](https://goreportcard.com/report/github.com/AllenDang/giu)
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 [![Go Reference](https://pkg.go.dev/badge/github.com/AllenDang/giu.svg)](https://pkg.go.dev/github.com/AllenDang/giu)