docs: add PR template, update bug report template (#1324)

* add pull request template with suggested task checklist
* add compiler version to bug report template (for installs built from src)

.github/ISSUE_TEMPLATE/bug_report.md

@@ -10,7 +10,7 @@ assignees: ''
 **Describe the bug**
 A clear and concise description of what the bug is.
 
-**To Reproduce**
+**To reproduce**
 Steps to reproduce the behavior:
 1. Go to '...'
 2. Click on '....'
@@ -23,6 +23,7 @@ A clear and concise description of what you expected to happen.
 **Screenshots**
 If applicable, add screenshots to help explain your problem.
 
-**Desktop (please complete the following information):**
- - OS: [e.g. macOS, Linux, Windows]
- - Version [e.g. 22]
+**Environment**
+ - Operating system (e.g. macOS, Linux, Windows) and version
+ - MODFLOW 6 version (if installed via distribution)
+ - Compiler toolchain/version (if built from source)

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

@@ -0,0 +1,8 @@
+Feel free to remove check-list items that aren't relevant to your change.
+
+- [ ] Closes #xxxx
+- [ ] Passed autotests
+- [ ] Formatted source files with `fprettify`
+- [ ] Updated definition (*.dfn) files with new or modified options
+- [ ] Described new options, features or behavior changes in release notes
+- [ ] Updated meson files, makefiles, and Visual Studio project files if new source files added