Move issue template

.github/ISSUE_TEMPLATE.md

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+### Explain the issue
+
+Most issues are related to bugs or problems. In these cases, you should
+include a minimal working example and a minimal vimrc file (see below), as
+well as:
+
+1. What vim version are you using?
+2. Steps to reproduce
+3. Expected behavior
+4. Observed behavior
+
+If your issue is instead a feature request or anything else, please
+consider if minimal examples and vimrc files might still be relevant.
+
+### Minimal working example
+
+Please provide a minimal working example, e.g.,
+
+```vim
+if l:x == 1
+  call one()
+elseif l:x == 2
+  call two()
+else
+  call three()
+endif
+```
+
+### Minimal vimrc file
+
+Please provide a minimal vimrc file that reproduces the issue. The
+following should often suffice:
+
+```vim
+set nocompatible
+
+" load match-up
+let &rtp  = '~/.vim/bundle/vim-matchup,' . &rtp
+let &rtp .= ',~/.vim/bundle/vim-matchup/after'
+
+" load other plugins, if necessary
+" let &rtp = '~/path/to/other/plugin,' . &rtp
+
+filetype plugin indent on
+syntax enable
+
+" match-up options go here
+```
+