add issue template (#4)

.github/ISSUE_TEMPLATE/bug-report.md

+---
+name: Bug Report
+about: Report a bug encountered while operating JuiceFS
+labels: kind/bug
+
+---
+
+<!-- Please use this template while reporting a bug and provide as much info as possible. Not doing so may result in your bug not being addressed in a timely manner. Thanks!
+-->
+
+
+**What happened**:
+
+**What you expected to happen**:
+
+**How to reproduce it (as minimally and precisely as possible)**:
+
+**Anything else we need to know?**:
+
+**Environment**:
+- JuiceFS version (use `./juicefs --version`):
+- Cloud provider or hardware configuration running JuiceFS:
+- OS (e.g: `cat /etc/os-release`):
+- Kernel (e.g. `uname -a`):
+- Object storage (cloud provider and region):
+- Redis info (version, cloud provider managed or self maintained):
+- Network connectivity (JuiceFS to Redis, JuiceFS to object storage):
+- Others:

.github/ISSUE_TEMPLATE/enhancement.md

+---
+name: Enhancement Request
+about: Suggest an enhancement to the JuiceFS project
+labels: kind/feature
+
+---
+<!-- Please only use this template for submitting enhancement requests -->
+
+**What would you like to be added**:
+
+**Why is this needed**:

.github/ISSUE_TEMPLATE/support.md

+---
+name: Support Request
+about: Support request or question relating to JuiceFS
+labels: kind/support
+
+---
+
+<!--
+STOP -- PLEASE READ!
+
+GitHub is not the right place for support requests.
+
+You can post your question on the [JuiceFS Slack](https://juicefs.slack.com/).
+-->
+