Create README.md (#5782)

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Co-authored-by: Julien Chaumond <chaumond@gmail.com>

model_cards/mrm8488/RoBERTinha/README.md

+---
+language: gl
+widget:
+- text: "Galicia é unha <mask> autónoma española."
+- text: "A lingua oficial de Galicia é o <mask>."
+---
+
+# RoBERTinha: RoBERTa-like Language model trained on OSCAR Galician corpus