docs: revise and fix some bits

CONTRIBUTING.md

@@ -35,7 +35,7 @@ source "$HOME/.cargo/env"
 ```bash
 git clone https://git.picodata.io/picodata/picodata/picodata.git
 cd picodata
-git submodule update --init
+git submodule update --init --recursive
 ```
 Compile the project:
 ```bash

README.md

 ## Picodata – Professional Data Management System for High Loads
-This repository contains the source code of Picodata, an in-memory distributed application server with a built-in database.
+This repository contains the source code of Picodata, a distributed application server with a built-in in-memory database.
 
 ### What is Picodata
 Picodata is a software for building professional data management systems. It provides a data storage system together with a development platform and a runtime for persistent applications written in Rust. Learn more about our software at the [picodata.io](picodata.io){:target="_blank"} web site.