Add CONTRIBUTING.md

Adds a contributing guide at the repo root following GitHub's community health file best practices, tailored to this repo's logo folder structure, metadata.md workflow, and auto-generated logo-data.js.

Author: ChrisMcKee1

CONTRIBUTING.md

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+# Contributing to Microsoft Cloud Product Logos
+
+First off — thank you! This repository is a community-maintained collection of
+current and legacy Microsoft cloud product logos, and it only stays useful
+because people like you help keep it accurate and complete.
+
+This guide explains how to contribute properly so your changes can be merged
+quickly and without rework. It complements the
+[Contributing section in the README](README.md#contributing) and the conventions
+described in [reorganisation_guidance.md](reorganisation_guidance.md).
+
+> **Trademark note:** All logos are the property of Microsoft Corporation and are
+> subject to [Microsoft's Trademark and Brand Guidelines](https://learn.microsoft.com/en-us/microsoft-365/cloud-storage-partner-program/online/branding).
+> This project simply collects them — **never alter or recreate the marks themselves.**
+
+---
+
+## Before you start
+
+Please **thoroughly check the repository first.** Many products have moved,
+been renamed, or have legacy versions tucked into sub-folders (see the structure
+rules below). Checking first avoids duplicate issues and pull requests.
+
+---
+
+## Ways to contribute
+
+| You want to… | Do this |
+| :--- | :--- |
+| Report an incorrect, outdated, or missing logo | [Open an issue](../../issues/new) |
+| Add a new logo | Open a pull request (see below) |
+| Update / replace an existing logo | Open a pull request (see below) |
+| Suggest a structural or process change | Open an issue to discuss first |
+
+If you spot something incorrect and know the fix, a pull request is welcome —
+otherwise an issue is perfectly fine.
+
+---
+
+## Adding or updating a logo
+
+### 1. Place the file in the correct folder
+
+- Logos live under `logos/` grouped by **product**, in a folder named after that
+  product.
+- Folder and file names are **lowercase**, use **hyphens** instead of spaces, and
+  contain **no spaces** (e.g. `microsoft-scout`, `azure-app-service`).
+- Group products by their current product family where applicable. Outliers
+  (e.g. Entra, Intune, Power BI) are handled case-by-case — see the
+  [README structure notes](README.md#file--folder-structure).
+- **Renamed products:** put the old logos in a sub-folder of the *current* name
+  (e.g. Yammer lives under `viva-engage`).
+- **Retired products:** move them into a `zzFORMER_PRODUCTS` folder within their
+  product family where possible.
+- **Multiple versions / eras:** keep older logos in sub-folders named by their
+  years of existence and style (e.g. `2019-current_full-color`).
+
+### 2. Follow the file naming convention
+
+- Prefer scalable vector art. Name single SVGs `<product>-scalable.svg`
+  (e.g. `microsoft-scout-scalable.svg`).
+- For raster files, include the dimensions in the filename where relevant
+  (e.g. `agent-365-300x300.png`).
+- Keep sizing/padding consistent with sibling files in the product family.
+
+### 3. Add or update `metadata.md`
+
+Every product folder contains a `metadata.md` file. The site
+([www.mscloudlogos.com](https://www.mscloudlogos.com)) is built from these files,
+so accurate metadata is essential.
+
+| Field | Description | Required |
+| :--- | :--- | :--- |
+| `name` | Current product name | Yes |
+| `type` | `Product`, `Family`, or `Feature` | Yes |
+| `status` | `Active`, `Retired`, or `Renamed (TO: <name>)` | Yes |
+| `altnames` | Alternative / former names, abbreviations (comma-separated) | No |
+| `prodfamilies` | Product family or families it belongs to (comma-separated) | No |
+
+Example:
+
+```text
+name: Microsoft Scout
+
+type: Product
+
+status: Active
+
+altnames: Scout, Frontier
+
+prodfamilies: Microsoft 365
+```
+
+See [reorganisation_guidance.md](reorganisation_guidance.md) for more worked
+examples (renamed products, families, and features).
+
+### 4. Do **not** hand-edit `docs/js/logo-data.js`
+
+`docs/js/logo-data.js` is **auto-generated** from the logo files and their
+`metadata.md` by [`generate-logo-data.py`](generate-logo-data.py). Never edit it
+by hand.
+
+You have two options:
+
+- **Let CI do it (simplest):** just commit your logo file(s) and `metadata.md`.
+  The [Update GitHub Pages workflow](.github/workflows/update-github-pages.yml)
+  regenerates and commits `logo-data.js` for branches in this repo, and comments
+  on fork pull requests asking you to regenerate it.
+- **Regenerate it yourself:** run the generator and commit the result:
+
+  ```bash
+  python generate-logo-data.py
+  ```
+
+> **Heads-up about the diff:** each logo's `id` in `logo-data.js` is a positional
+> index. Adding a logo renumbers the IDs of everything after it, so the generated
+> diff can look large. **This is expected** — the IDs aren't referenced by the
+> website (lookups use `productSlug` and `path`), and CI produces the same result.
+
+---
+
+## Submitting your pull request
+
+1. **Fork** the repository and create a descriptive branch
+   (e.g. `add-microsoft-scout-logo`).
+2. Make your changes following the conventions above.
+3. Keep each pull request focused — one product or one logical change is ideal.
+4. Write a clear PR title and description explaining what you added or fixed, and
+   where you sourced the logo if relevant.
+5. Open the pull request against the `main` branch and respond to any review
+   feedback.
+
+---
+
+## Sources
+
+Official Microsoft icon sets are linked in the
+[References and sources section of the README](README.md#references-and-sources).
+When possible, use official sources and note where a logo came from in your PR.
+
+Thanks again for contributing! 🎉