Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Report a bug and help us improve stochtree
+title: "[BUG]"
+labels: bug
+assignees: ''
+
+---
+
+# Description
+A clear and concise description of what the bug is. Please include details on whether you're using R or Python and which model you're using (i.e. BART, BCF, custom model).
+
+# Reproducing
+If possible, include the precise steps to reproduce the behavior. If not, just describe in as much detail how this error showed up for you. Something like
+1. Generate data via 
+```
+set.seed(1234)
+```
+2. Run BART via 
+```
+bart_model = bart(X_train = X, y_train = y, ...)
+```
+3. See error
+
+# Expected behavior
+A clear and concise description of what you expected to happen.
+
+# Screenshots
+If applicable, add screenshots to help explain your problem.
+
+# System (please complete the following information):
+ - OS: [e.g. iOS]
+ - Browser [e.g. chrome, safari]
+ - Version [e.g. 22]
+
+# Additional context
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/documentation_update.md

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+---
+name: Documentation update
+about: Help us improve stochtree's documentation
+title: "[DOCS]"
+labels: documentation
+assignees: ''
+
+---
+
+**Describe the update you'd like to see to the docs**
+A clear and concise description of how the documentation falls short. E.g. I want to do [...] but cannot figure out how, or the documentation gives conflicting advice
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest a new feature for stochtree
+title: "[FEATURE]"
+labels: enhancement
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.