templates: added issue template

(cherry picked from commit a0e2e22a4f)

.github/CONTRIBUTING.md

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+If you'd like to contribute to go-ethereum please fork, fix, commit and
+send a pull request. Commits who do not comply with the coding standards
+are ignored (use gofmt!). If you send pull requests make absolute sure that you
+commit on the `develop` branch and that you do not merge to master.
+Commits that are directly based on master are simply ignored.
+
+See [Developers' Guide](https://github.com/ethereum/go-ethereum/wiki/Developers'-Guide)
+for more details on configuring your environment, testing, and
+dependency management.

.github/ISSUE_TEMPLATE.md

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+#### System information
+
+Geth version: `geth version`
+OS & Version: Windows/Linux/OSX
+Commit hash : (if `develop`)
+
+#### Expected behaviour
+
+
+#### Actual behaviour
+
+
+#### Steps to reproduce the behaviour
+
+
+#### Backtrace
+
+````
+[backtrace]
+````