chore: add issue and PR TEMPLATES (#60)

.github/ISSUE_TEMPLATE/bug.md

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+---
+name: Report a bug
+about: Something with opBNB is not working as expected
+title: ''
+labels: 'type:bug'
+assignees: ''
+---
+
+#### System information
+
+Network: `mainnet`/`testnet`/`local`
+
+if you are running a local node, please provide the following information:
+op-node version: `op-node version`
+op-geth version: `op-node -v`
+OS & Version: Windows/Linux/OSX
+
+#### Expected behaviour
+
+
+#### Actual behaviour
+
+
+#### Steps to reproduce the behaviour
+
+
+#### Backtrace
+
+````
+[backtrace]
+````
+
+When submitting logs: please submit them as text and not screenshots.

.github/ISSUE_TEMPLATE/feature.md

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+---
+name: Request a feature
+about: Report a missing feature - e.g. as a step before submitting a PR
+title: ''
+labels: 'type:feature'
+assignees: ''
+---
+
+# Rationale
+
+Why should this feature exist?
+What are the use-cases?
+
+# Implementation
+
+Do you have ideas regarding the implementation of this feature?
+Are you willing to implement this feature?

.github/ISSUE_TEMPLATE/question.md

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+---
+name: Ask a question
+about: Something is unclear
+title: ''
+labels: 'type:docs'
+assignees: ''
+---
+
+This should only be used in very rare cases e.g. if you are not 100% sure if something is a bug or asking a question that leads to improving the documentation. For general questions please use [discord](https://discord.gg/bnbchain).

.github/PULL_REQUEST_TEMPLATE.md

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+### Description
+
+add a description of your changes here...
+
+### Rationale
+
+tell us why we need these changes...
+
+### Example
+
+add an example CLI or API response...
+
+### Changes
+
+Notable changes:
+* add each change in a bullet point here
+* ...