Add Pull Request Template (#1366)

* added PULL_REQUEST_TEMPLATE.md

* moved ISSUE_TEMPLATE and ISSUE_TEMPLATE to .github

* moved PULL_REQUEST_TEMPLATE.md file to .github

Author: iamrajiv

.github/ISSUE_TEMPLATE.md

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+# The gRPC-Gateway project is maintained by volunteers in their spare time. Please follow these troubleshooting steps before submitting an issue.
+
+- [ ] Check if your issue has already been reported (https://github.com/grpc-ecosystem/grpc-gateway/issues).
+- [ ] Update your protoc to the [latest version](https://github.com/google/protobuf/releases).
+- [ ] Update your copy of the `grpc-gateway` library to the latest version from github:
+  ```sh
+  go get -u github.com/grpc-ecosystem/grpc-gateway
+  ```
+- [ ] Delete the `protoc-gen-grpc-gateway` and `protoc-gen-swagger` binary from your `PATH`,
+  and reinstall the latest versions:
+  ```sh
+  go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway
+  go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-swagger
+  ```
+  
+## I still have a problem!
+ 
+Please consider reaching out for help on a chat forum, such as
+[Gophers Slack](https://invite.slack.golangbridge.org/) (channel #grpc-gateway).
+It's much easier to help with common debugging steps in a chat, and some of
+the maintainers are reading the channel regularly. If you
+submit an issue which is clearly an environment setup problem, or it's obvious
+you haven't tried seeking help somewhere else first, we may close your issue.
+ 
+## I still have a problem!
+
+Please follow these steps to submit a bug report:
+
+### Bug reports:
+
+Fill in the following sections with explanations of what's gone wrong.
+
+### Steps you follow to reproduce the error:
+
+```html
+<!-- Example steps
+1.  I grab my catapult
+2.  I load it with lettuce
+3.  Press the fire button
+4.  It falls over
+-->
+```
+
+Your steps here.
+
+### What did you expect to happen instead:
+
+```html
+<!-- Example answer
+1.  It would have rained lettuce from the sky bringing forth a cuddly army of bunnies we could
+    play with
+-->
+```
+
+Your answer here.
+
+### What's your theory on why it isn't working:
+
+```html
+<!-- Example answer
+Evil wizards are hoarding the bunnies and don't want to share. The wizards are casting 
+lettuce protection spells so the catapult won't work.
+-->
+```
+
+Your theory here.

.github/PULL_REQUEST_TEMPLATE.md

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+<!--
+Thank you for sending the PR! We appreciate you spending the time to work on these changes.
+
+Help us understand your motivation by explaining why you decided to make this change.
+
+You can learn more about contributing to grpc-gateway here: https://github.com/grpc-ecosystem/grpc-gateway/blob/master/CONTRIBUTING.md
+
+Happy contributing!
+
+-->
+
+#### References to other Issues or PRs
+
+<!-- If this pull request fixes an issue, write "Fixes #NNNN" in that exact
+format, e.g. "Fixes #1234" (see
+https://tinyurl.com/auto-closing for more information). Also, please
+write a comment on that issue linking back to this pull request once it is
+open. -->
+
+#### Have you read the [Contributing Guidelines](https://github.com/grpc-ecosystem/grpc-gateway/blob/master/CONTRIBUTING.md)?
+
+#### Brief description of what is fixed or changed
+
+#### Other comments