Update issue templates

- Revise "Bug Report"
- Add "Help Wanted"
- Select appropriate tag for each issue template

Author: caic99

.github/ISSUE_TEMPLATE/bug-report.md

@@ -2,25 +2,33 @@
 name: Bug Report
 about: Create a report for problems with ABACUS
 title: ''
-labels: bug
+labels: Bug
 assignees: dyzheng
 
 ---
 
 ## Describe the Bug
-A clear and concise description of what the bug is.
+A clear and concise description of what the bug is. 
+The bug may results in:
+- abnormal interruption of the program,
+- systematic or randomized numerical error, or
+- relatively low efficiency.
+
+## Expected behavior
+A clear and concise description of what you expected to happen.
 
 ## To Reproduce
 Steps to reproduce the behavior:
 1. [e.g. clone the source code from ...]
 2. [e.g. configure CMake with options ...]
 3. [e.g. build ABACUS with ...]
 4. [e.g. run ABACUS with ...]
+It is recommended to attach your calculation case here for the developers to reproduce the bug.
 
 ## Environment
-- OS: [e.g. CentOS 7.6]
-- Compiler: [e.g. Intel LLVM 2021.1]
-- Optional Dependencies: [e.g. Intel MKL]
+- OS: [e.g. Ubuntu 20.04]
+- Compiler: [e.g. gcc 5.1.0]
+- Dependencies: [e.g. Intel MKL, OpenBLAS]
 
 ## Additional Context
 Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature-request.md

@@ -0,0 +1,17 @@
+---
+name: Feature Request
+about: Suggest something more for ABACUS to do
+title: ''
+labels: Feature
+assignees: mohanchen
+
+---
+
+## Background
+A clear and concise description of why this new feature is important.
+
+## Describe the solution you'd like
+A clear and concise description of what you want to happen.
+
+## Additional context
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/help-wanted.md

@@ -0,0 +1,10 @@
+---
+name: Help Wanted
+about: For general questions or assistance.
+title: ''
+labels: Help wanted
+assignees: caic99
+
+---
+
+Want to use ABACUS for certain system? Facing problems when installing ABACUS? Don't know how to choose a good parameter? Feel free to reach us, and we'll do our best to help!

.github/ISSUE_TEMPLATE/software-enhancements.md

@@ -2,14 +2,16 @@
 name: Software Enhancements
 about: Suggest an idea to make ABACUS more robust and organized
 title: ''
-labels: enhancement
+labels: Refactor
 assignees: caic99
 
 ---
 
 ## Describe Current Status and Possible Solution
 
-A clear and concise description of why this enhancement is important. If you have some ideas about how to achieve it, please also describe.
+A clear and concise description of why this enhancement is important. 
+Describing the current situation of ABACUS is preferred.
+If you have some ideas about how to achieve it, please feel free to comment.
 
 ## Additional Context