add onboarding documentation

get-started.mdx

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+---
+title: Introduction
+slug: ../
+---
+
+## Try now
+
+Go to [excalidraw.com](https://excalidraw.com) to start sketching.
+
+## How are these docs structured
+
+These docs are focused on developers, and structured in the following way:
+
+- [Introduction](/docs/) — development setup and introduction.
+- [Onboarding](/docs/introduction/onboarding) — first-week setup and ramp-up guide for new engineers.
+- [@excalidraw/excalidraw](/docs/@excalidraw/excalidraw/installation) — docs for the npm package to help you integrate Excalidraw into your own app.
+- Editor — IN PROGRESS. Docs describing the internals of the Excalidraw editor to help in contributing to the codebase.
+- [@excalidraw/mermaid-to-excalidraw](/docs/@excalidraw/mermaid-to-excalidraw/installation) - Docs for the mermaid to excalidraw parser

onboarding.mdx

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+# Onboarding for New Engineers
+
+This guide helps new employees become productive in the Excalidraw monorepo quickly, with practical setup steps, codebase orientation, and a suggested first-week path.
+
+## What You Are Working In
+
+Excalidraw uses a monorepo with two main product surfaces:
+
+- `packages/excalidraw/` - the published React package `@excalidraw/excalidraw`.
+- `excalidraw-app/` - the full web app (the code that powers excalidraw.com).
+
+Supporting packages used by the editor live in `packages/`:
+
+- `@excalidraw/common`
+- `@excalidraw/element`
+- `@excalidraw/math`
+- `@excalidraw/utils`
+
+```text
+excalidraw/
+|- excalidraw-app/            # product app
+|- packages/
+|  |- excalidraw/             # npm package
+|  |- common/
+|  |- element/
+|  |- math/
+|  `- utils/
+|- dev-docs/                  # this documentation site
+`- examples/                  # integration examples
+```
+
+## Architecture At A Glance
+
+```mermaid
+flowchart LR
+  A[Excalidraw App<br/>excalidraw-app] --> B[@excalidraw/excalidraw]
+  B --> C[@excalidraw/element]
+  B --> D[@excalidraw/common]
+  B --> E[@excalidraw/math]
+  B --> F[@excalidraw/utils]
+  G[Examples] --> B
+```
+
+Use this mental model:
+
+- If it is app-specific behavior, investigate `excalidraw-app/`.
+- If it should be reusable by consumers, implement in `packages/excalidraw/` or a core package.
+
+## Local Setup
+
+### Prerequisites
+
+- Node.js
+- Yarn (workspace-aware)
+- Git
+
+### One-time setup
+
+```bash
+git clone https://github.com/excalidraw/excalidraw.git
+cd excalidraw
+yarn
+```
+
+### Start development
+
+```bash
+yarn start
+```
+
+Then open `http://localhost:3000`.
+
+## Daily Development Workflow
+
+1. Pull latest changes and sync your branch.
+1. Run the app with `yarn start`.
+1. Make a focused change in the appropriate package/app area.
+1. Run quality gates before opening a PR:
+   - `yarn test:typecheck`
+   - `yarn test:update`
+   - `yarn fix` (if needed)
+
+## Typical Change Routing
+
+```mermaid
+flowchart TD
+  S[Start from issue or task] --> Q{Where does it belong?}
+  Q -->|Reusable editor behavior| P[packages/excalidraw or core packages]
+  Q -->|App-only UX/integration| A[excalidraw-app]
+  P --> T[Run tests and typecheck]
+  A --> T
+  T --> R[Open PR]
+```
+
+## First Week Ramp-Up Plan
+
+### Day 1
+
+- Complete local setup and run `yarn start`.
+- Read `introduction/development` and `introduction/contributing`.
+- Skim root `README.md` for product context.
+
+### Day 2-3
+
+- Pick a small issue (or shadow one) and trace code path from UI to data model.
+- Make a small documentation or bugfix PR to validate workflow end-to-end.
+
+### Day 4-5
+
+- Implement one scoped change with tests.
+- Request review early, incorporate feedback, and document what you learned.
+
+## Collaboration and Expectations
+
+- Prefer small, reviewable PRs over large batches.
+- Include tests for bug fixes and non-trivial features.
+- Ask for early alignment when changing shared editor behavior.
+- Keep docs updated when behavior or APIs change.
+
+## Debugging and Validation Checklist
+
+Before requesting review, verify:
+
+- [ ] App runs locally (`yarn start`).
+- [ ] Type checks pass (`yarn test:typecheck`).
+- [ ] Tests and snapshots are updated (`yarn test:update`).
+- [ ] Formatting/lint checks are clean (`yarn fix` as needed).
+- [ ] Manual smoke test of changed behavior in browser.
+
+## Useful Pointers
+
+- Development guide: `/docs/introduction/development`
+- Contribution guide: `/docs/introduction/contributing`
+- Package docs: `/docs/@excalidraw/excalidraw/installation`
+- Mermaid parser docs: `/docs/@excalidraw/mermaid-to-excalidraw/installation`