docs: add issue template

.github/ISSUE_TEMPLATE/decompilation-error.md

+---
+name: Decompilation error
+about: Create a report to help us improve jadx decompiler
+title: "[core]"
+labels: Core, bug
+assignees: ''
+
+---
+
+**Checks before report**
+- [ ] check [latest unstable build](https://bintray.com/skylot/jadx/unstable/_latestVersion#files) (maybe issue already fixed)
+- [ ] search existing issues by exception message
+ (for example `JadxRuntimeException: Can't find immediate dominator for block`)
+- [ ] check [Troubleshooting Q&A](https://github.com/skylot/jadx/wiki/Troubleshooting-Q&A) section on wiki
+
+**Describe error**
+- provide full name of method or class with error
+- provide full java stacktrace
+
+  **Note**: no need to copy method fallback code (commented pseudocode)
+- attach or provide link to apk file (double check apk version)
+
+  **Note**: GitHub don't allow attach files with `.apk` extension, but you can change extension by adding `.zip` at the end :)