Merge pull request #1156 from flowforge/json-use-case

Create json use case

src/_includes/core-nodes/json-use-case.md

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+## What's the JSON node in Node-RED used for?
+
+The JSON node in Node-RED is used for processing JavaScript Object Notation (JSON) data. It allows you to convert between a JSON-formatted string and a JavaScript object, making it highly versatile for tasks involving JSON manipulation. This conversion capability proves to be essential when working with APIs, storing data, or transmitting data between different services.
+
+## Use Case: Monitoring Equipment Efficiency
+
+Suppose you have a JSON data stream that comes from different sensors installed on an assembly line in a manufacturing plant. The JSON objects include data such as equipment name, timestamp, and efficiency percentage. You'd like to extract this information and calculate a daily average efficiency for each equipment to help in predictive maintenance and to optimize the production process.
+
+**JSON Input:**
+```json
+{
+  "equipment": "Drill Press",
+  "timestamp": "2023-09-22T12:34:56Z",
+  "efficiency": 89.5
+}
+```
+### Flow
+
+<iframe width="100%" height="100%" src="https://flows.nodered.org/flow/f2d01d981b0dcb8b33d01785a39fef3c/share" allow="clipboard-read; clipboard-write" style="border: none;"></iframe>