Add that ingest endpoint accepts application/json (#314)

Author: tothmano

restapi/ingest.mdx

@@ -183,7 +183,7 @@ To send data to Axiom in NDJSON format:
 1. Encode the events as JSON objects.
 1. Enter each JSON object in a separate line into the body of the API request.
 1. Optional: In the body of the request, set optional parameters such as `timestamp-field` and `timestamp-format`. For more information, see the [ingest data API reference](/restapi/endpoints/ingestIntoDataset).
-1. Set the `Content-Type` header to `application/x-ndjson`.
+1. Set the `Content-Type` header to either `application/json` or `application/x-ndjson`.
 1. Set the `Authorization` header to `Bearer API_TOKEN`. Replace `API_TOKEN` with the Axiom API token you have generated. 
 1. Send the POST request to `https://api.axiom.co/v1/datasets/DATASET_NAME/ingest`. Replace `DATASET_NAME` with the name of the Axiom dataset where you want to send data.