Creating a readme for ALBERT in Mongolian (#4603)

Here I am uploading Mongolian masked language model (ALBERT) on your platform.
https://en.wikipedia.org/wiki/Mongolia

model_cards/bayartsogt/albert-mongolian/README.md

+# ALBERT-Mongolian
+[pretraining repo link](https://github.com/bayartsogt-ya/albert-mongolian)
+## Model description
+Here we provide pretrained ALBERT model and trained SentencePiece model for Mongolia text. Training data is the Mongolian wikipedia corpus from Wikipedia Downloads and Mongolian News corpus.
+
+## Evaluation Result:
+```
+loss = 1.7478163
+masked_lm_accuracy = 0.6838185
+masked_lm_loss = 1.6687671
+sentence_order_accuracy = 0.998125
+sentence_order_loss = 0.007942731
+```
+
+## Fine-tuning Result on Eduge Dataset:
+```
+                precision    recall  f1-score   support
+
+  байгал орчин       0.83      0.76      0.80       483
+     боловсрол       0.79      0.75      0.77       420
+         спорт       0.98      0.96      0.97      1391
+     технологи       0.85      0.83      0.84       543
+       улс төр       0.88      0.87      0.87      1336
+    урлаг соёл       0.89      0.94      0.91       726
+         хууль       0.87      0.83      0.85       840
+   эдийн засаг       0.80      0.84      0.82      1265
+    эрүүл мэнд       0.84      0.90      0.87       562
+
+      accuracy                           0.87      7566
+     macro avg       0.86      0.85      0.86      7566
+  weighted avg       0.87      0.87      0.87      7566
+```
+
+## Reference
+1. [ALBERT - official repo](https://github.com/google-research/albert)
+2. [WikiExtrator](https://github.com/attardi/wikiextractor)
+3. [Mongolian BERT](https://github.com/tugstugi/mongolian-bert)
+4. [ALBERT - Japanese](https://github.com/alinear-corp/albert-japanese)
+5. [Mongolian Text Classification](https://github.com/sharavsambuu/mongolian-text-classification)
+6. [You's paper](https://arxiv.org/abs/1904.00962)
+
+## Citation
+```
+@misc{albert-mongolian,
+  author = {Bayartsogt Yadamsuren},
+  title = {ALBERT Pretrained Model on Mongolian Datasets},
+  year = {2020},
+  publisher = {GitHub},
+  journal = {GitHub repository},
+  howpublished = {\url{https://github.com/bayartsogt-ya/albert-mongolian/}}
+}
+```
+
+## For More Information
+Please contact by bayartsogtyadamsuren@icloud.com