Add issue templates (#1862)

* Add issue templates

Fixes #1468

* Apply suggestions from code review

* Update bug_report.md

* Update feature_request.md

* Update rendering-bug-report.md

* Update bug_report.md

* Update bug_report.md

* Update rendering-bug-report.md

* Update bug_report.md

* Update rendering-bug-report.md

* Apply suggestions from code review

* Update feature_request.md

* Apply suggestions from code review

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,39 @@
+---
+name: Bug report
+about: Report functionality that isn't working as it should (other than just poor rendering)
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+> Before reporting a bug
+- [ ] Check [common issues](https://katex.org/docs/issues.html).
+- [ ] Check the bug is reproducible in [the demo](https://katex.org). If not, check KaTeX is up-to-date and installed correctly.
+- [ ] Search for [existing issues](https://github.com/KaTeX/KaTeX/issues).
+
+**Describe the bug:**
+A clear and concise description of what the bug is. If your installation is available on the web or you can provide a minimal repo or CodePen that reproduces the bug, please add the link to it.
+
+**To Reproduce:**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. 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.
+
+**Environment (please complete the following information):**
+ - KaTeX Version: [Can be checked via `katex.version`]
+ - Device: [e.g. Desktop, iPhone 8]
+ - OS: [e.g. Windows 10, iOS 11]
+ - Browser: [e.g. Chrome, Safari]
+ - Version: [e.g. 72]
+
+**Additional context:**
+Add any other context about the problem here. If you're using a library to use KaTeX, please include its name and setup.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,25 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: enhancement
+assignees: ''
+
+---
+
+> Before requesting a feature, please search for [existing issues](https://github.com/KaTeX/KaTeX/issues).
+
+**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.
+
+**Link to or name of a (La)TeX package that provides the same feature:**
+KaTeX's general goal is to render as LaTeX does.
+
+**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.

.github/ISSUE_TEMPLATE/rendering-bug-report.md

@@ -0,0 +1,38 @@
+---
+name: Rendering bug report
+about: Report functionality that renders incorrectly/poorly
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+> Before reporting a bug
+- [ ] Check [common issues](https://katex.org/docs/issues.html).
+- [ ] Check the bug is reproducible in [the demo](https://katex.org). If not, check KaTeX is up-to-date and installed correctly.
+- [ ] Search for [existing issues](https://github.com/KaTeX/KaTeX/issues).
+
+**Describe the bug:**
+A clear and concise description of what the bug is. If your installation is available on the web or you can provide a minimal repo or CodePen that reproduces the bug, please add the link to it.
+
+**(La)TeX code:**
+The code of (La)TeX you tried to render:
+```latex
+
+```
+
+**Expected behavior:**
+A clear and concise description of what you expected to happen. KaTeX's general goal is to render as LaTeX does, so if possible, please include a LaTeX rendering. You can obtain one using [QuickLaTeX](https://www.quicklatex.com/).
+
+**Screenshots:**
+If applicable, add screenshots to help explain your problem.
+
+**Environment (please complete the following information):**
+ - KaTeX Version: [Can be checked via `katex.version`]
+ - Device: [e.g. Desktop, iPhone 8]
+ - OS: [e.g. Windows 10, iOS 11]
+ - Browser: [e.g. Chrome, Safari]
+ - Version: [e.g. 72]
+
+**Additional context:**
+Add any other context about the problem here. If you're using a library to use KaTeX, please include its name and setup.