Add CONTRIBUTING.md file

CONTRIBUTING.md

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+## File issues
+The best way to get started with a contribution is to start a dialog with us. Sometimes features will be under development or out of scope for this library and it's best to check before starting work on contribution, especially for large work items.
+
+## Pull requests
+All pull requests should be submitted against the **main** branch or a specific feature branch. The `main` branch is intended to represent the code released in the most-recent npm package.
+
+When a new package is about to be released, the release PR will be merged into `main`. The package will be generated from `main`.
+
+## Commit message format
+
+To support our automated release process, pull requests are required to follow the [Conventional Commit](https://www.conventionalcommits.org/en/v1.0.0/)
+format.
+
+Each commit message consists of a **header**, an optional **body** and an optional **footer**. The header is the first line of the commit and
+MUST have a **type** (see below for a list of types) and a **description**. An optional **scope** can be added to the header to give extra context.
+
+```
+<type>[optional scope]: <short description>
+<BLANK LINE>
+<optional body>
+<BLANK LINE>
+<optional footer(s)>
+```
+
+The recommended commit types used are:
+
+ - **feat** for feature updates (increments the _minor_ version)
+ - **fix** for bug fixes (increments the _patch_ version)
+ - **perf** for performance related changes e.g. optimizing an algorithm
+ - **refactor** for code refactoring changes
+ - **test** for test suite updates e.g. adding a test or fixing a test
+ - **style** for changes that don't affect the meaning of code. e.g. formatting changes
+ - **docs** for documentation updates e.g. ReadMe update or code documentation updates
+ - **build** for build system changes (gradle updates, external dependency updates)
+ - **ci** for CI configuration file changes e.g. updating a pipeline
+ - **chore** for miscellaneous non-sdk changes in the repo e.g. removing an unused file
+
+Adding a footer with the prefix **BREAKING CHANGE:** will cause an increment of the _major_ version.
+
+Some things to note about this project:
+
+### How the library is built
+The TypeScript client library has a handwritten set of files in the folder `src/graphclient`, all other files in the folder `src` are models and request builders generated using the [Kiota](https://github.com/microsoft/kiota). **Changes made to the generated folders will be overwritten** the next time the generator is run. 
+```suggestion
+# Contributing
+```
+
+### How the generator works
+You can view the [README](https://github.com/microsoft/kiota/blob/main/README.md) for a full run-through of its capabilities.
+
+The generator runs through an OpenAPI-compliant metadata file maintained by Microsoft Graph (https://github.com/microsoftgraph/msgraph-metadata/blob/master/openapi/v1.0/openapi.yaml).
+
+### When new features are added to the library
+Generation happens as part of a manual process that occurs once a significant change or set of changes has been added to the Graph. This may include:
+ - A new workload comes to v1.0 of Graph (Microsoft Teams, Batching, etc.)
+ - There is significant addition of functionality (Delta Queries, etc.)
+
+However, this is evaluated on a case-by-case basis. If the library is missing v1.0 Graph functionality that you wish to utilize, please [file an issue](https://github.com/microsoftgraph/msgraph-sdk-typescript/issues).
+
+We do our best to prevent breaking changes from being introduced into the library during this process. If you find a breaking change, please file an issue and we will work to get this resolved ASAP.