microRTPS_transport.h: add clarifying comment for Transport_node::write()

msg/templates/urtps/microRTPS_transport.h

@@ -45,8 +45,22 @@ public:
 	virtual int init() {return 0;}
 	virtual uint8_t close() {return 0;}
 	ssize_t read(uint8_t *topic_ID, char out_buffer[], size_t buffer_len);
+
+	/**
+	 * write a buffer
+	 * @param topic_ID
+	 * @param buffer buffer to write: it must leave get_header_length() bytes free at the beginning. This will be
+	 *               filled with the header. length does not include get_header_length(). So buffer looks like this:
+	 *                -------------------------------------------------
+	 *               | header (leave free)          | payload data     |
+	 *               | get_header_length() bytes    | length bytes     |
+	 *                -------------------------------------------------
+	 * @param length buffer length excluding header length
+	 * @return length on success, <0 on error
+	 */
 	ssize_t write(const uint8_t topic_ID, char buffer[], size_t length);
-	/* Get the Length of struct Header to make headroom for the size of struct Header alongwith payload*/
+
+	/** Get the Length of struct Header to make headroom for the size of struct Header along with payload */
 	ssize_t get_header_length();
 
 protected: