docs(tests): update documentation to include system testing for zephyr

Signed-off-by: SorinO <sorin.olari2@gmail.com>

Author: SorinOlari

docs/tests/SystemTests.md

@@ -4,15 +4,17 @@ System Tests are tests designed to test the entire system as a black box,
 including all components and dependencies.
 We usually build it in release mode, so we test exactly what we are delivering.
 
-Currently, these are only available for the POSIX platform.
+Currently, these are available for POSIX and Zephyr platforms.
 
 However, these are also sometimes reused for memory [leak checks](LeakChecks.md) and [source code coverage generation](CoverageReports.md).
 In these cases, Ocre needs to be built with instrumentation so it is not testing the release build.
 For more information on those, refer to their specific documentation.
 
 These tests are configured in the CI workflows as a quality gate. All PRs must pass all of them.
 
-## Build and run
+## Linux
+
+### Build and run
 
 Create a build directory and navigate to it:
 
@@ -47,7 +49,7 @@ You can also run the individual test executable binaries `test_*` in the build d
 
 Note that the tests must be run from the build directory, because they look for images in the current working directory + `./ocre/src/ocre/var/lib/ocre/images/`.
 
-## Details
+### Details
 
 The individual test binaries:
 
@@ -62,3 +64,34 @@ Follow a similar pattern. `test_lib` is testing the general library initializati
 `test_container` tests the specific functionality of a specific container.
 
 Please, refer to their source code for more details.
+
+## Zephyr
+
+### Build and run
+To build the Zephyr system tests for the `native_sim_64` board:
+
+```sh
+west build -p always -b native_sim/native/64 tests/system/zephyr/context
+```
+
+Replace `context` with `container`, `lib`, or `ocre` to build different tests:
+
+- `tests/system/zephyr/lib` - Tests the general library initialization functions
+- `tests/system/zephyr/ocre` - Tests the Ocre library and management of contexts
+- `tests/system/zephyr/context` - Tests context functionality, creating and managing the lifetime of containers
+- `tests/system/zephyr/container` - Tests the specific functionality of a container
+
+To run the test:
+```sh
+west build -t run
+```
+
+The last lines of the output will be something like:
+```
+-----------------------
+25 Tests 0 Failures 0 Ignored 
+OK
+```
+
+### Details
+Each test must be run individually. Run the build command for one test at a time, then execute `west build -t run` to run that specific test.