Update issue templates (#4278)

Author: topecongiro

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,26 @@
+---
+name: Bug report
+about: Report rustfmt errors, failing to format inputs, etc.
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+**Describe the bug**
+
+<!-- A clear and concise description of what the bug is. -->
+
+**To Reproduce**
+
+<!-- Steps to reproduce the behavior. If possible, please provide us with a link to your project or a minimal working example. -->
+
+**Expected behavior**
+
+<!-- A clear and concise description of what you expected to happen. -->
+
+**Meta**
+
+- rustfmt version: <!-- `rustfmt -V` -->
+- From where did you install rustfmt?: <!-- rustup, crates.io, package managers, etc. -->
+- How do you run rustfmt: <!-- `rustfmt`, `cargo-fmt`, via editors, etc. -->

.github/ISSUE_TEMPLATE/formatting-issues.md

@@ -0,0 +1,28 @@
+---
+name: Formatting issues
+about: Poor formatting issues
+title: ''
+labels: poor-formatting
+assignees: topecongiro
+
+---
+
+**Input**
+
+```rust
+```
+
+**Output**
+
+```rust
+```
+
+**Expected output**
+
+```rust
+```
+
+**Meta**
+
+- rustfmt version: <!-- `rustfmt -V` -->
+- From where did you install rustfmt?: <!-- rustup, crates.io, package managers, etc. -->