Update CONTRIBUTING.md

Author: vlad-perevezentsev

CONTRIBUTING.md

@@ -191,3 +191,41 @@ these steps:
 >    ```
 >    The error is related to the `tcl` package. You should uninstall the `tcl`
 > package to resolve the error.
+
+## Error handler
+
+Use the `DPCTL_VERBOSITY` environment variable to show errors of different severity levels of the C-API in the console.
+You can specify one of the following severity levels (in increasing order of severity): `warning` and `error`.
+
+```bash
+export DPCTL_VERBOSITY=error
+```
+
+Messages of a given severity are shown not only in the console for that severity, but also for a lower severity.For example, the severity level `error` will output severity errors for `error` and `warning` to the console.
+
+## Google logging libriry (glog)
+
+The dpctl error handler provides logging for exceptions of different severity levels in `libsyclinterface` using the [glog](https://github.com/google/glog) library.
+To use logging during development , follow these steps:
+
+1. Install glog package of the latest version (0.5.0)
+     ```bash
+    conda install glog
+    ```
+2. Build dpctl with glog support
+     ```bash
+    python scripts/build_locally.py --oneapi --glog
+    ```
+3. Use `DPCTLService_InitLogger` and `DPCTLService_ShutdownLogger` functions during development to initialize the Google's logging library and de-initialize accordingly
+
+      ```bash
+      DPCTLService_InitLogger(const char *app_name, const char *log_dir);
+      DPCTLService_ShutdownLogger();
+      ```
+
+ - `*app_name` - name of the executable file (prefix for logs of various levels).
+ - `*log_dir` - directory path for writing log files.
+
+> **_NOTE:_**
+>
+> If `InitGoogleLogging` is not called for initialization, glog will turn into `logtostderr` mode and log files will not be generated.