Update github templates (#3510)

An ISSUE_TEMPLATE directory was added, meaning the ISSUE_TEMPLATE.md is
now obsolete. Remove stale.yml because not used. Symlink CONTRIBUTING.md
the other way around to get GitHub recognize it.

Signed-off-by: Miek Gieben <miek@miek.nl>

.github/CONTRIBUTING.md

@@ -0,0 +1,81 @@
+# Contributing to CoreDNS
+
+Welcome! Our community focuses on helping others and making CoreDNS the best it can be. We gladly
+accept contributions and encourage you to get involved!
+
+## Bug Reports
+
+First, please [search this
+repository](https://github.com/coredns/coredns/search?q=&type=Issues&utf8=%E2%9C%93) with a variety
+of keywords to ensure your bug is not already reported.
+
+If not, [open an issue](https://github.com/coredns/coredns/issues) and answer the questions so we
+can understand and reproduce the problematic behavior.
+
+The burden is on you to convince us that it is actually a bug in CoreDNS. This is easiest to do when
+you write clear, concise instructions so we can reproduce the behavior (even if it seems obvious).
+The more detailed and specific you are, the faster we will be able to help you. Check out [How to
+Report Bugs Effectively](https://www.chiark.greenend.org.uk/~sgtatham/bugs.html).
+
+Please be kind. :smile: Remember that CoreDNS comes at no cost to you, and you're getting free help.
+
+## Minor Improvements and New Tests
+
+Submit [pull requests](https://github.com/coredns/coredns/pulls) at any time. Make sure to write
+tests to assert your change is working properly and is thoroughly covered.
+
+## New Features
+
+First, please [search](https://github.com/coredns/coredns/search?q=&type=Issues&utf8=%E2%9C%93) with
+a variety of keywords to ensure your suggestion/proposal is new.
+
+Please also check for existing pull requests to see if someone is already working on this. We want
+to avoid duplication of effort.
+
+If the proposal is new and no one has opened pull request yet, you may open either an issue or a
+pull request for discussion and feedback.
+
+If you are going to spend significant time implementing code for a pull request, best to open an
+issue first and "claim" it and get feedback before you invest a lot of time.
+
+**If someone already opened a pull request, but you think the pull request has stalled and you would
+like to open another pull request for the same or similar feature, get some of the maintainers (see
+[CODEOWNERS](CODEOWNERS)) involved to resolve the situation and move things forward.**
+
+If possible make a pull request as small as possible, or submit multiple pull request to complete a
+feature. Smaller means: easier to understand and review. This in turn means things can be merged
+faster.
+
+## New Plugins
+
+A new plugin is (usually) about 1000 lines of Go. This includes tests and some plugin boiler plate.
+This is a considerable amount of code and will take time to review. To prevent too much back and
+forth it is advisable to start with the plugin's `README.md`; This will be its main documentation
+and will help nail down the correct name of the plugin and its various config options.
+
+From there it can work its way through the rest (`setup.go`, the `ServeDNS` handler function, etc.).
+Doing this will help the reviewers, as each chunk of code is relatively small.
+
+Also read [plugin.md](https://raw.githubusercontent.com/coredns/coredns/master/plugin.md) for
+advice on how to write a plugin.
+
+## Updating Dependencies
+
+We use [Go Modules](https://github.com/golang/go/wiki/Modules) as the tool to manage vendor dependencies.
+
+Use the following to update the version of all dependencies
+```sh
+$ go get -u
+```
+
+After the dependencies have been updated or added, you might run the following to
+cleanup the go module files:
+```sh
+$ go mod tidy
+```
+
+Please refer to [Go Modules](https://github.com/golang/go/wiki/Modules) for more details.
+
+# Thank You
+
+Thanks for your help! CoreDNS would not be what it is today without your contributions.

CONTRIBUTING.md

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+.github/CONTRIBUTING.md