Update issue templates

.github/ISSUE_TEMPLATE/custom.md

+---
+name: Custom issue template
+about: Describe this issue template's purpose here.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+

.github/ISSUE_TEMPLATE/feature_request.md

----
-name: Feature request
-about: Suggest an idea for this project
-title: ''
-labels: ''
-assignees: ''
-
----
-
-**Is your feature request related to a problem? Please describe.**
-A clear and concise description of what the circumstance is and what the associated problem is. Ex. I'm using TDengine for this use case: [...]. But I'm always frustrated when [...]
-
-**Describe your desired behavior**
-A clear and concise description of what you want to happen. Ex. I want TDengine to be able to do [...] when I try to do [...] with it.
-
-**Describe your solutions/suggestions if you've any**
-A clear and concise description of any solutions/suggestions to this problem or features you've considered.
-
-**Additional context**
-Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/general-questions.md

+---
+name: General Questions
+about: General questions about TDengine's usage, user experiences, milestones etc.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**General Questions**
+A general question should be related to TDengine's user's manual, user experience, milestones, business cooperations etc. 
+Before you ask a question, please:
+1. Try searching for answers in the official documentation
+2. Try searching in the existing issues on GitHub
+3. Try searching on tech forums such as Stack Overflow, Quora, CSDN, v2ex etc.
+4. Try using online searching engines such as Google, Bing, Baidu
+
+If all the ways above couldn't help, please clearly and concisely describe what the question is.

.github/ISSUE_TEMPLATE/performance-related-questions.md

+---
+name: Performance-related Questions
+about: Any questions related to TDengine's performance.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Performance Issue** 
+Any questions related to TDengine's performance can be discussed here.
+
+**Problem Description** 
+A clear and concise description of what the problem is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Database parameters used: 
+ ```show databases```
+2. Verbs used: Insert/Import/Select?
+3. Describe the total amount of data
+4. Observed performance vs. expected performance
+
+**Screenshots**
+ If applicable, add screenshots to help explain your problem.
+
+**Environment (please complete the following information):**
+
+* OS: [e.g. CentOS 7.0]
+* Memory, CPU, current Disk Space
+* TDengine Version [e.g. 1.6.1.7]
+
+**Additional Context** 
+Add any other context about the problem here.