Add multipart form data section to README

README.md

@@ -77,6 +77,29 @@ By performing a simple HTTP GET or POST request to that endpoint, your specified
 
 However, hook defined like that could pose a security threat to your system, because anyone who knows your endpoint, can send a request and execute your command. To prevent that, you can use the `"trigger-rule"` property for your hook, to specify the exact circumstances under which the hook would be triggered. For example, you can use them to add a secret that you must supply as a parameter in order to successfully trigger the hook. Please check out the [Hook rules page](docs/Hook-Rules.md) for detailed list of available rules and their  usage.
 
+## Multipart Form Data
+
+[webhook][w] provides limited support the parsing of multipart form data.
+Upon receiving a `multipart/form-data` request, [webhook][w] steps through the named parts and parses all parts that match one of the following criteria:
+
+1. The `Content-Type` header is a supported type (only JSON is supported so far).
+1. The part is named in the `parse-parameters-as-json` setting.
+
+The named part will be accessible from the `payload` source by referencing the name of the part.
+For example, given a named part of "command", a match rule could look similar to the following:
+
+```json
+{
+  "match": {
+    "type": "value",
+    "parameter": {
+      "source": "payload",
+      "name": "command.event",
+    },
+    "value": "media.play"
+}
+```
+
 ## Templates
 [webhook][w] can parse the `hooks.json` input file as a Go template when given the `-template` [CLI parameter](docs/Webhook-Parameters.md). See the [Templates page](docs/Templates.md) for more details on template usage.