[DOCS][Layer Tests] Update layer test documentation (openvinotoolkit#…

…23485)

**Details:** Update layer test documentation. It will be used by
external developers and mentioned in GFIs.

**Ticket:** TBD

---------

Signed-off-by: Kazantsev, Roman <[email protected]>
Co-authored-by: Anastasiia Pnevskaia <[email protected]>

tests/layer_tests/README.md

@@ -1,34 +1,47 @@
-# Layer tests
+# Layer Tests
 
-This folder layer tests framework code and test files.
+The layer tests primarily aim to validate support for PyTorch, TensorFlow, TensorFlow Lite, and ONNX frameworks' operations by OpenVINO.
+The test pipeline includes the following steps:
+1. Creation of a model with the tested operation using original framework API
+2. Conversion of the created model using OpenVINO's `convert_model` method
+3. Inference of both the original and converted models using the framework and OpenVINO on random input data
+4. Checking whether the inference results from OpenVINO and the framework are the same or different within a tolerance threshold
 
-## Getting Started
+## Setup Environment
 
-#### Pre-requisites
-
-* OpenVINO should be configured as usual.
-
-#### Setup
-
-* Install requirements:
-    ```bash
-    pip3 install -r requirements.txt
+To set up the environment for launching layer tests, perform the following steps:
+1. Install the OpenVINO wheel package. If you're testing changes in OpenVINO, build your local wheel package for installation.
+Find instructions on how to build on [wiki page](https://github.com/openvinotoolkit/openvino/blob/master/docs/dev/build.md).
+    ```sh
+    pip install openvino.whl
     ```
-* Set up environment variables for layer tests (if you use wheel package path to python api could be removed):
-    ```bash
-    export PYTHONPATH="path_to_openvino"/tests/layer_tests/:"path_to_openvino"/tools/mo:"path to python api"
+2. (Optional) Install the OpenVINO Tokenizers wheel package if you're testing the support of operations using conversion and operation extensions from OpenVINO Tokenizers.
+If you're testing changes in OpenVINO Tokenizers, build your local wheel package for installation.
+Find instructions on how to build on [GitHub page](https://github.com/openvinotoolkit/openvino_tokenizers)
+    ```sh
+    pip install openvino_tokenizers.whl
     ```
-* If there is need to use specific libs it is possible to specify path to them using OV_LIBRARY_PATH env variable
-    ```bash
-    export OV_LIBRARY_PATH="path_to_libs"
+3. Install requirements for running layer tests.
+    ```sh
+    cd tests/layer_tests
+    pip install -r requirements.txt
     ```
-* To parametrize tests by device and precision (optional)
-   ```bash
+
+## Run Tests
+
+Set environment variables `TEST_DEVICE` and `TEST_PRECISION` to select device and inference precision for OpenVINO inference. Allowed values for `TEST_DEVICE` are `CPU` and `GPU`. Allowed values for `TEST_PRECISION` are `FP32` and `FP16`.
+
+Example to run the TensorFlow layer test for the `tf.raw_ops.Unique` operation on CPU with default inference precision for device:
+   ```sh
+   cd tests/layer_tests
+   export TEST_DEVICE="CPU"
+   pytest tensorflow_tests/test_tf_Unique.py
+   ```
+
+Example to run the PyTorch layer test for the `torch.linalg.cross` operation on CPU and GPU with `FP16` and `FP32` inference precisions:
+   ```sh
+   cd tests/layer_tests
    export TEST_DEVICE="CPU;GPU"
    export TEST_PRECISION="FP32;FP16"
+   pytest pytorch_tests/test_cross.py
    ```
-
-## Run tests
-```bash
-py.test
-```