add readme explaining EJ api behavior

Author: CarsonDavis

environmental_justice/README.md

@@ -0,0 +1,86 @@
+# Environmental Justice API
+
+## Overview
+This API provides access to Environmental Justice data from multiple sources. It supports retrieving data from individual sources or as a combined dataset with defined precedence rules.
+
+## Endpoints
+
+### GET /api/environmental-justice/
+
+Retrieves environmental justice data based on specified data source.
+
+#### Query Parameters
+
+| Parameter    | Description | Default    | Options                                      |
+|-------------|-------------|------------|----------------------------------------------|
+| data_source | Data source filter | "combined" | "spreadsheet", "ml_production", "ml_testing", "combined" |
+
+#### Data Source Behavior
+
+1. **Single Source**
+   - `?data_source=spreadsheet`: Returns only spreadsheet data
+   - `?data_source=ml_production`: Returns only ML production data
+   - `?data_source=ml_testing`: Returns only ML testing data
+
+2. **Combined Data** (Default)
+   - Access via `?data_source=combined` or no parameter
+   - Merges data from 'spreadsheet' and 'ml_production' sources
+   - Precedence rules:
+     - If the same dataset exists in both sources, the spreadsheet version is used
+     - Unique datasets from ml_production are included
+     - ML testing data is not included in combined view
+
+#### Example Requests
+
+```bash
+# Get combined data (default)
+GET /api/environmental-justice/
+
+# Get combined data (explicit)
+GET /api/environmental-justice/?data_source=combined
+
+# Get only spreadsheet data
+GET /api/environmental-justice/?data_source=spreadsheet
+
+# Get only ML production data
+GET /api/environmental-justice/?data_source=ml_production
+
+# Get only ML testing data
+GET /api/environmental-justice/?data_source=ml_testing
+```
+
+#### Response Fields
+
+Each record includes the following fields:
+- dataset
+- description
+- description_simplified
+- indicators
+- intended_use
+- latency
+- limitations
+- project
+- source_link
+- strengths
+- format
+- geographic_coverage
+- data_visualization
+- spatial_resolution
+- temporal_extent
+- temporal_resolution
+- sde_link
+- data_source
+
+## Data Source Definitions
+
+- **spreadsheet**: Primary source data from environmental justice spreadsheets
+- **ml_production**: Production machine learning processed data
+- **ml_testing**: Testing/staging machine learning processed data
+
+## Precedence Rules
+When retrieving combined data:
+1. If a dataset exists in both spreadsheet and ml_production:
+   - The spreadsheet version takes precedence
+   - The ml_production version is excluded
+2. Datasets unique to ml_production are included in the response
+3. ML testing data is never included in combined results