Separate issue templates, add support doc (#25705)

* Update issue template to break down by bug and template, add support doc to close #23133

* add links from readme for bug and feature templates

.github/ISSUE_TEMPLATE/bug.md

@@ -0,0 +1,11 @@
+Before opening:
+
+- [Search for duplicate or closed issues](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue)
+- [Validate](https://html5.validator.nu/) and [lint](https://github.com/twbs/bootlint#in-the-browser) any HTML to avoid common problems
+- Read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/master/CONTRIBUTING.md)
+
+Bug reports must include:
+
+- Operating system and version (Windows, Mac OS X, Android, iOS, Win10 Mobile)
+- Browser and version (Chrome, Firefox, Safari, IE, MS Edge, Opera 15+, Android Browser)
+- [Reduced test case](https://css-tricks.com/reduced-test-cases/) and suggested fix using [CodePen](https://codepen.io/) or [JS Bin](https://jsbin.com/)

.github/ISSUE_TEMPLATE/feature.md

@@ -0,0 +1,9 @@
+Before opening:
+
+- [Search for duplicate or closed issues](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue)
+- Read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/master/CONTRIBUTING.md)
+
+Feature requests must include:
+
+- As much detail as possible for what we should add and why it's important to Bootstrap
+- Relevant links to prior art, screenshots, or live demos whenever possible

.github/SUPPORT.md

@@ -0,0 +1,11 @@
+### Bug reports
+
+See the [contributing guidelines](CONTRIBUTING.md) for sharing bug reports.
+
+### How-to
+
+For general troubleshooting or help getting started:
+
+- Join [the official Slack room](https://bootstrap-slack.herokuapp.com/).
+- Chat with fellow Bootstrappers in IRC. On the `irc.freenode.net` server, in the `##bootstrap` channel.
+- Ask and explore Stack Overflow with the [`bootstrap-4`](https://stackoverflow.com/questions/tagged/bootstrap-4) tag.

README.md

@@ -11,9 +11,13 @@
     <a href="https://getbootstrap.com/docs/4.0/"><strong>Explore Bootstrap docs »</strong></a>
     <br>
     <br>
-    <a href="https://themes.getbootstrap.com/">Bootstrap Themes</a>
+    <a href="https://github.com/twbs/bootstrap/issues/new?template=bug.md">Report bug</a>
     ·
-    <a href="https://jobs.getbootstrap.com/">Job Board</a>
+    <a href="https://github.com/twbs/bootstrap/issues/new?template=feature.md&labels=feature">Request feature</a>
+    ·
+    <a href="https://themes.getbootstrap.com/">Themes</a>
+    ·
+    <a href="https://jobs.getbootstrap.com/">Jobs</a>
     ·
     <a href="https://blog.getbootstrap.com/">Blog</a>
   </p>