Create an issue form (#5238)

This fixes #5229 (Issue templates no longer working):

Seems that the templates need to be put into `.github/ISSUE_TEMPLATE/`, and that `.github/ISSUE_TEMPLATE.md` does not work anymore.

We could use the opportunity to turn this into [an issue form](https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/configuring-issue-templates-for-your-repository#creating-issue-templates) (which would make it much less likely to get those issues with all the placeholders left as-are, I'd hope).

Author: dscho

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,64 @@
+ - [ ] I was not able to find an [open](https://github.com/git-for-windows/git/issues?q=is%3Aopen) or [closed](https://github.com/git-for-windows/git/issues?q=is%3Aclosed) issue matching what I'm seeing
+
+### Setup
+
+ - Which version of Git for Windows are you using? Is it 32-bit or 64-bit?
+
+```
+$ git --version --build-options
+
+** insert your machine's response here **
+```
+
+ - Which version of Windows are you running? Vista, 7, 8, 10? Is it 32-bit or 64-bit?
+
+```
+$ cmd.exe /c ver
+
+** insert your machine's response here **
+```
+
+ - What options did you set as part of the installation? Or did you choose the
+   defaults?
+
+```
+# One of the following:
+> type "C:\Program Files\Git\etc\install-options.txt"
+> type "C:\Program Files (x86)\Git\etc\install-options.txt"
+> type "%USERPROFILE%\AppData\Local\Programs\Git\etc\install-options.txt"
+> type "$env:USERPROFILE\AppData\Local\Programs\Git\etc\install-options.txt"
+$ cat /etc/install-options.txt
+
+** insert your machine's response here **
+```
+
+ - Any other interesting things about your environment that might be related
+   to the issue you're seeing?
+
+** insert your response here **
+
+### Details
+
+ - Which terminal/shell are you running Git from? e.g Bash/CMD/PowerShell/other
+
+** insert your response here **
+
+ - What commands did you run to trigger this issue? If you can provide a
+   [Minimal, Complete, and Verifiable example](http://stackoverflow.com/help/mcve)
+   this will help us understand the issue.
+
+```
+** insert your commands here **
+```
+ - What did you expect to occur after running these commands?
+
+** insert here **
+
+ - What actually happened instead?
+
+** insert here **
+
+ - If the problem was occurring with a specific repository, can you provide the
+   URL to that repository to help us with testing?
+
+** insert URL here **