Update issue templates

Issue templates have been added.

.github/ISSUE_TEMPLATE/bug_report.md

+---
+name: Bug report
+about: Create a report to help us improve
+
+---
+
+<!--
+If you are reporting a new issue, make sure that we do not have any duplicates
+already open. You can ensure this by searching the issue list for this
+repository. If there is a duplicate, please close your issue and add a comment
+to the existing issue instead.
+
+Use the commands below to provide key information from your environment:
+You do NOT have to include this information if this is a FEATURE REQUEST
+-->
+
+**Description**
+
+<!--
+Briefly describe the problem you are having in a few paragraphs.
+-->
+
+**Steps to reproduce the issue:**
+1.
+2.
+3.
+
+**Describe the results you received:**
+
+**Describe the results you expected:**
+
+**Output of `go version`:**
+
+```text
+(paste your output here)
+```
+
+**Excelize version or commit ID:**
+
+```text
+(paste here)
+```
+
+**Environment details (OS, Microsoft Excel™ version, physical, etc.):**

.github/ISSUE_TEMPLATE/feature_request.md

+---
+name: Feature request
+about: Suggest an idea for this project
+
+---
+
+<!--
+If you are reporting a new issue, make sure that we do not have any duplicates
+already open. You can ensure this by searching the issue list for this
+repository. If there is a duplicate, please close your issue and add a comment
+to the existing issue instead.
+
+Use the commands below to provide key information from your environment:
+You do NOT have to include this information if this is a FEATURE REQUEST
+-->
+
+**Description**
+
+<!--
+Briefly describe the problem you are having in a few paragraphs.
+-->
+
+**Steps to reproduce the issue:**
+1.
+2.
+3.
+
+**Describe the results you received:**
+
+**Describe the results you expected:**
+
+**Output of `go version`:**
+
+```text
+(paste your output here)
+```
+
+**Excelize version or commit ID:**
+
+```text
+(paste here)
+```
+
+**Environment details (OS, Microsoft Excel™ version, physical, etc.):**