Add GitHub issue template

Closes #216.

This should make it easier for people to file high-quality issues.
Tweaked CONTRIBUTING.md accordingly, and fixed a stale reference to
mbland/custom-links.

Author: mbland

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,30 @@
+## Due diligence
+
+- [ ] I am familiar with the ["Reporting issues" section of
+  CONTRIBUTING.md][reporting]
+- [ ] I have searched the [existing issues][issues] and haven't found one
+  that matches what I'm reporting or requesting now.
+- [ ] If this is a bug report, I have searched the [Bash changelog][changes]
+  for information that may explain or provide clues to the behavior I'm
+  observing and reference it in the body of the report.
+
+[reporting]: https://github.com/mbland/go-script-bash/blob/master/CONTRIBUTING.md#reporting-issues
+[issues]:    https://github.com/mbland/go-script-bash/issues
+[changes]:   https://tiswww.case.edu/php/chet/bash/CHANGES
+
+## Framework, Bash, and operating system version information
+
+```
+If this is a bug report, replace this preformatted section with the output from:
+
+$ ./go goinfo
+
+Otherwise remove this section altogether.
+```
+
+## Description
+
+Replace this text with a description of your bug report or feature request.
+
+If this is a bug report, include any relevant command line steps, code snippets,
+or test cases to reproduce the issue.

CONTRIBUTING.md

@@ -66,7 +66,7 @@ been filed.
 
 If you do find one...
 
-[issues]: https://github.com/mbland/custom-links/issues
+[issues]: https://github.com/mbland/go-script-bash/issues
 
 ### Do not add a +1 comment!
 
@@ -84,10 +84,11 @@ matching issue...
 Try to be as specific as possible about your environment and the problem you're
 observing. At a minimum, include:
 
-- The version of bash you're using, from either `bash --version` or `echo
-  $BASH_VERSION`
-- The version of the go-script-bash library you're using
+- The output from `./go goinfo`
 - Command line steps or code snippets that reproduce the issue
+- Any apparently relevant information from the [Bash changelog][bash-changes]
+
+[bash-changes]: https://tiswww.case.edu/php/chet/bash/CHANGES
 
 Also consider using: