New model addition issue template

.github/ISSUE_TEMPLATE/--new-model-addition.md

+---
+name: "\U0001F31FNew model addition"
+about: Submit a proposal/request to implement a new Transformer-based model
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+# 🌟New model addition
+
+## Model description
+
+<!-- Important information -->
+
+## Open Source status
+
+* [ ] the model implementation is available: (give details)
+* [ ] the model weights are available: (give details)
+
+## Additional context
+
+<!-- Add any other context about the problem here. -->

.github/ISSUE_TEMPLATE/bug-report.md

 ---
 name: "\U0001F41B Bug Report"
 about: Submit a bug report to help us improve PyTorch Transformers
+title: ''
+labels: ''
+assignees: ''
+
 ---
 
 ## 🐛 Bug

.github/ISSUE_TEMPLATE/feature-request.md

 ---
 name: "\U0001F680 Feature Request"
 about: Submit a proposal/request for a new PyTorch Transformers feature
+title: ''
+labels: ''
+assignees: ''
+
 ---
 
 ## 🚀 Feature

.github/ISSUE_TEMPLATE/migration.md

 ---
 name: "\U0001F4DA Migration from PyTorch-pretrained-Bert"
 about: Report a problem when migrating from PyTorch-pretrained-Bert to Transformers
+title: ''
+labels: ''
+assignees: ''
+
 ---
 
 ## 📚 Migration

.github/ISSUE_TEMPLATE/question-help.md

 ---
 name: "❓Questions & Help"
 about: Start a general discussion related to PyTorch Transformers
+title: ''
+labels: ''
+assignees: ''
+
 ---
 
 ## ❓ Questions & Help