SECURITY-10891: improve readme

Author: dsztanko

README.md

@@ -6,6 +6,26 @@ Java implementation of the [Escher](https://github.com/emartech/escher) HTTP req
 Prerequisite
 ------------
 
+If you clone the repository for the first time, run the following commands to initialize the test cases as well:
+```shell
+# after git clone stay in the root of the project
+git submodule init
+git submodule update
+```
+
+Update the repository with the following command to have the test cases as well:
+```shell
+git pull origin master --recurse-submodules
+```
+
+To update the remote test cases to the latest state, run the following:
+```shell
+ git submodule update --remote test-cases
+```
+
+Development
+-------------
+
 In order to compile the project, **Maven** and **JDK 11** (or above) are needed.
 
 To check if maven is configured properly, run the `mvn --version` command and look at the line beginning with *Java version*.