feat: add how to contribute

Author: Sigmanificient

HOW_TO_CONTRIBUTE.md

@@ -0,0 +1,89 @@
+Here’s a concise `HOW_TO_CONTRIBUTE.md` for adding a new OAuth service to your project based on the Discord example:
+
+---
+
+# How to Contribute a New OAuth Service
+
+This guide explains how to add a new OAuth service to our platform using the existing Discord integration as a reference.
+
+## 1. Create a Config Model
+
+In your service module, create a `Config` Pydantic model that defines the OAuth configuration:
+
+```python
+from pydantic import BaseModel
+
+class Config(BaseModel):
+    service: str = "google"
+    client_id: str
+    client_secret: str
+    auth_base: str = "..."
+    token_url: str = "..."
+    api_base: str = "..."
+    api_resource: str = "..."
+    profile_endpoint: str = "..."
+    redirect_uri: str = "..."
+    scope: str = "..."
+    pkce: bool = True
+```
+
+* Set `service` to a unique identifier for the platform.
+* Specify the authorization URL (`auth_base`), token URL (`token_url`), API endpoints, and scopes.
+* `redirect_uri` should point to your API route for handling the callback.
+
+## 2. Instantiate the OAuth Provider
+
+Use the shared `OAuthProvider` class:
+
+```python
+from fastapi import APIRouter
+import pathlib
+from .oauth_base import OAuthProvider
+
+router = APIRouter(prefix="/[my_service]", tags=["[my_service]"])
+
+provider = OAuthProvider(
+    package=__package__,
+    config_model=Config,
+    icon=(pathlib.Path(__file__).parent / "icon.svg").read_text()
+)
+```
+
+* The `icon` will be displayed in the frontend service cards.
+
+## 3. Add API Routes
+
+Define FastAPI routes to handle connecting, authentication, token refresh, and user info:
+
+```python
+@router.get("/connect")
+async def google_connect(token: str, platform: str):
+    return await provider.connect(token, platform)
+
+@router.get("/auth")
+async def google_auth(code: str, state: str, db=Depends(get_session)):
+    return await provider.auth(code, state, db)
+
+@router.get("/refresh")
+async def google_refresh(user=Depends(get_current_user), db=Depends(get_session)):
+    return await provider.refresh(user, db)
+
+@router.get("/me")
+async def google_me(user=Depends(get_current_user), db=Depends(get_session)):
+    return await provider.me(user, db)
+```
+
+* `/connect` initiates the OAuth connection.
+* `/auth` handles the callback from the OAuth provider.
+* `/refresh` refreshes the access token.
+* `/me` retrieves the current user’s profile info from the service.
+
+## 4. Add Service Icon
+
+Place an SVG icon named `icon.svg` in the service module folder. This will be displayed in the frontend cards for connecting services.
+
+## 5. Test
+
+1. Login in to the area
+2. Go to `/services`
+3. You should see you newly added service and be able to connect to it