📝 add contributing.md

Author: aagarwal1012

CONTRIBUTING.md

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+Contributing to IntroViews-Flutter
+==========================
+:+1::tada: First off, thanks for taking the time to contribute! :tada::+1:  
+If you'd like to report a bug or join in the development
+of IntroViews-Flutter, then here are some notes on how to do that.
+
+## Contents
+* [Reporting bugs and opening issues](#reporting-bugs-and-opening-issues)
+* [Coding Guidelines](#coding-guidelines)
+    * [Pull Requests](#pull-requests)
+    * [MVP architecture](#mvp-architecture)
+    * [Style Check](#style-check)
+    * [Git Commit Messages](#git-commit-messages)
+* [MDG Chat Room](#mdg-chat-room)
+* [Security](#security)
+  
+## Reporting bugs and opening issues
+
+If you'd like a report a bug or open an issue then please:
+
+**Check if there is an existing issue.** If there is then please add
+   any more information that you have, or give it a 👍.
+
+When submitting an issue please describe the issue as clearly as possible, including how to
+reproduce the bug, which situations it appears in, what you expected to happen, and what actually happens.
+If you can include a screenshot for front end issues that is very helpful.
+
+## Coding Guidelines
+
+### Pull Requests
+We love pull requests, so be bold with them! Don't be afraid of going ahead
+and changing something, or adding a new feature. We're very happy to work with you
+to get your changes merged into IntroViews-Flutter.
+
+If you've got an idea for a change then please discuss it in the open first, 
+either by opening an issue, or by joining us in our
+[MDG public chat room](https://mdg.sdslabs.co/chat) or email me at [[email protected]](mailto:[email protected]).
+
+If you're looking for something to work on, have a look at the open issues in the repository [here](https://github.com/aagarwal1012/IntroViews-Flutter/issues).
+
+> We don't have a set format for Pull requests, but we expect you to list changes, bugs generated and other relevant things in PR message.
+
+### MVP architecture
+IntroViews-Flutter is built keeping [MVP (model-view-presenter)](https://en.wikipedia.org/wiki/Model–view–presenter) architecture in mind, so any changes that are proposed to IntroViews-Flutter should follow MVP architecture. If you are confused regarding where a method should be, join us at  [MDG public chat room](https://mdg.sdslabs.co/chat), we'll be happy to help.
+
+### Style Check
+IntroViews-Flutter uses `dartfmt`  for performing style checks on the codebase, which helps us in maintaining the quality of the code. Please check that the code is properly formatted according to `dartfmt` and also resolve all the issues, if any, shown by `dart analyze` before making a pull request. **Pull Requests will only be merged once all the violations are resolved**.
+
+### Git Commit Messages
+* Use the present tense ("Add feature" not "Added feature")
+* Use the imperative mood ("Move cursor to..." not "Moves cursor to...")
+* Limit the first line to 72 characters or less
+* Reference issues and pull requests liberally
+* When only changing documentation, include `[ci skip]` in the commit description
+* Consider starting the commit message with an applicable emoji:
+    * :art: `:art:` when improving the format/structure of the code
+    * :racehorse: `:racehorse:` when improving performance
+    * :non-potable_water: `:non-potable_water:` when plugging memory leaks
+    * :memo: `:memo:` when writing docs
+    * :bug: `:bug:` when fixing a bug
+    * :fire: `:fire:` when removing code or files
+    * :green_heart: `:green_heart:` when fixing the CI build
+    * :white_check_mark: `:white_check_mark:` when adding tests
+    * :lock: `:lock:` when dealing with security
+    * :arrow_up: `:arrow_up:` when upgrading dependencies
+    * :arrow_down: `:arrow_down:` when downgrading dependencies
+    * :shirt: `:shirt:` when removing linter warnings
+
+## MDG Chat Room
+
+If you want to ask any questions in real-time, or get a feel for what's going on
+then please drop into our [MDG public chat room](https://mdg.sdslabs.co/chat).
+If no one is online then you can still leave a message that will hopefully get a reply
+when we return.
+
+## Security
+
+Please do not publish security vulnerabilities publicly until we've had a chance
+to address them. All security related issues/patches should be sent directly to
+[[email protected]](mailto:[email protected]) where we will attempt to address them quickly. If you're
+unsure whether something is a security issue or not, then please be cautious and contact us at [[email protected]](mailto:[email protected]) first.