PHY: updated README to include PHY testvector use

Author: ofontbach

README.md

@@ -89,3 +89,19 @@ cmake ..
 make
 make test
 ```
+
+Run PHY testvector tests:
+
+A number of PHY tests are based on MATLAB generated testvectors. By default, those tests are disabled.
+The following steps are required to enable them:
+
+1. Download the [PHY testvector set](https://github.com/srsran/srsRAN_Project/releases/phy_testvectors.tar.gz).
+2. Copy the PHY testvectors to its location within srsRAN:
+```
+tar -xzf phy_testvectors.tar.gz -C /path_to_your_local_repository/srsgnb/
+```
+3. Enable the use of PHY testvectors by modifying the root [CMakeLists](CMakeLists.txt) as shown below:
+```
+option(USE_PHY_TESTVECTORS   "Enable testvector PHY tests"              ON)
+```
+4. Do a fresh srsRAN build.