Update issue labels and pull request template (#2)

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,13 +15,17 @@ Please put an x in the boxes related to your change.
 
 *Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.*
 
-- [ ] I have read the [CONTRIBUTING](https://github.com/klaytn/caver-java/blob/master/CONTRIBUTING.md) doc
+- [ ] I have read the [CONTRIBUTING GUIDELINES](https://github.com/klaytn/caver-java/blob/master/CONTRIBUTING.md) doc
 - [ ] I have signed the [CLA](https://cla-assistant.io/klaytn/caver-java)
 - [ ] Lint and unit tests pass locally with my changes
 - [ ] I have added tests that prove my fix is effective or that my feature works
 - [ ] I have added necessary documentation (if appropriate)
 - [ ] Any dependent changes have been merged and published in downstream modules
 
+## Related issues
+
+- Please leave the issue numbers or links related to this PR here.
+
 ## Further comments
 
 If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

CONTRIBUTING.md

@@ -45,25 +45,25 @@ You can use the following labels:
 
 Labels for initial issue categories:
 
-- bug: Issues with the code-level bugs.
-- documentation: Issues with the documentation.
-- enhancement: Issues for enhancement requests.
+- issue/bug: Issues with the code-level bugs.
+- issue/documentation: Issues with the documentation.
+- issue/enhancement: Issues for enhancement requests.
 
 Status of open issues (will be tagged by the project moderators):
 
 - (no label): The default status.
-- need more information : The issue's creator needs to provide additional information to review.
-- reviewing: The issue is under review.
-- re-label needed: The label needs to be changed to confirmed as being a `bug` or future `enhancement`.
-- approved: The issue is confirmed as being a `bug` to be fixed or `enhancement` to be developed.
-- contribution welcome: The fix or enhancement is approved and you are invited to contribute to it.
+- open/need more information : The issue's creator needs to provide additional information to review.
+- open/reviewing: The issue is under review.
+- open/re-label needed: The label needs to be changed to confirmed as being a `bug` or future `enhancement`.
+- open/approved: The issue is confirmed as being a `bug` to be fixed or `enhancement` to be developed.
+- open/contribution welcome: The fix or enhancement is approved and you are invited to contribute to it.
 
 Status of closed issues:
 
-- fixed: A fix for the issue was provided.
-- duplicate: The issue is also reported in a different issue and is being managed there.
-- invalid: The issue cannot be reproduced.
-- reject: The issue is rejected after review.
+- closed/fixed: A fix for the issue was provided.
+- closed/duplicate: The issue is also reported in a different issue and is being managed there.
+- closed/invalid: The issue cannot be reproduced.
+- closed/reject: The issue is rejected after review.
 
 ### Code Contribution