github: update issue templates (#2552)

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,36 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: A-tokio, C-bug
+assignees: ''
+
+---
+
+**Version**
+List the versions of all `tokio` crates you are using. The easiest way to get
+this information is using `cargo-tree`.
+
+`cargo install cargo-tree`
+(see install here: https://github.com/sfackler/cargo-tree)
+
+Then:
+
+`cargo tree | grep tokio`
+
+**Platform**
+The output of `uname -a` (UNIX), or version and 32 or 64-bit (Windows)
+
+**Description**
+Enter your issue details here.
+One way to structure the description:
+
+[short summary of the bug]
+
+I tried this code:
+
+[code sample that causes the bug]
+
+I expected to see this happen: [explanation]
+
+Instead, this happened: [explanation]