update emqx tagline and what is emqx section

Author: id

emqx/README-short.txt

@@ -1 +1 @@
-An Open-Source, Cloud-Native, Distributed MQTT Message Broker for IoT.
+The most scalable open-source MQTT broker for IoT, IIoT, connected vehicles, and more.

emqx/content.md

@@ -1,8 +1,12 @@
 # What is EMQX
 
-[EMQX MQTT broker](https://emqx.io/products/broker) is a fully open source, highly scalable, highly available distributed MQTT messaging broker for IoT, M2M and Mobile applications that can handle tens of millions of concurrent clients.
+[EMQX](https://emqx.io/) is the world's most scalable open-source MQTT broker with a high performance that connects 100M+ IoT devices in 1 cluster, while maintaining 1M message per second throughput and sub-millisecond latency.
 
-Starting from 3.0 release, *EMQX* broker fully supports MQTT V5.0 protocol specifications and backward compatible with MQTT V3.1 and V3.1.1, as well as other communication protocols such as MQTT-SN, CoAP, LwM2M, WebSocket and STOMP. The 3.0 release of the *EMQX* broker can scaled to 10+ million concurrent MQTT connections on one cluster.
+EMQX supports multiple open standard protocols like MQTT, HTTP, QUIC, and WebSocket. It's 100% compliant with MQTT 5.0 and 3.x standard, and secures bi-directional communication with MQTT over TLS/SSL and various authentication mechanisms.
+
+With the built-in powerful SQL-based rules engine, EMQX can extract, filter, enrich and transform IoT data in real-time. In addition, it ensures high availability and horizontal scalability with a masterless distributed architecture, and provides ops-friendly user experience and great observability.
+
+EMQX boasts more than 20K+ enterprise users across 50+ countries and regions, connecting 100M+ IoT devices worldwide, and is trusted by over 400 customers in mission-critical scenarios of IoT, IIoT, connected vehicles, and more, including over 70 Fortune 500 companies like HPE, VMware, Verifone, SAIC Volkswagen, and Ericsson.
 
 %%LOGO%%
 
@@ -13,7 +17,7 @@ Starting from 3.0 release, *EMQX* broker fully supports MQTT V5.0 protocol speci
 Execute some command under this docker image
 
 ```console
-$ docker run -d --name emqx %%IMAGE%%:tag
+$ docker run -d --name emqx %%IMAGE%%:${tag}
 ```
 
 For example