HowToUseLoggers.md (#332)

Create HowToUseLoggers.md

Author: JaneEugenia

HowToUseLoggers.md

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+# How to use loggers in UTBotJava
+
+If you develop different modules of our project like CE, CLI or else, you might need to use loggers or even add your own ones to UTBot. 
+<br/> Let\`s see how you can work with it. 🙂
+
+🟢**1. Find out where appropriate log4j2.xml configuration file is**
+
+It depends on two factors:
+
+- Find the project you will run. For instance, for Idea plugin it is **_utbot-intellij_** subproject
+- Chose appropriate log4j2.xml. If you are going to run tests for framework, it\`s in the test folder of utbot-framework subproject.
+
+The file is usually in the resource folder. 
+<br/>
+<br/>
+<br/>
+🟢**2. Find out the logger name**
+
+The easiest way is:
+
+- Go in the code that you are going to debug. Let’s assume it is a method in com.home.utbot.framework.plugin.api.UtBotTestCaseGenerator.
+- Find out if there is a KotlinLogging object that is used to create a **logger**
+- If such a logger exists, use the fully qualified class name as the logger name in the next steps
+<br/>
+
+🟢**3. Add logger**
+
+Open log4j2.xml and add the logger in the loggers section like this
+
+```
+<Logger name=" com.home.utbot.framework.plugin.api.UtBotTestCaseGenerator " level="info">
+    <AppenderRef ref="Console"/>
+</Logger>
+```
+<br/>
+<br/>
+
+🟢**4. Logger level**
+
+Depending on the desired amount of information, change the **level** attribute. If you do not see output in the console, the wrong level value could be the reason. The **trace** is most verbose level. 
+<br/>
+<br/>
+
+🟢**5. Output**
+
+Sometimes the logging information could be printed in a wrong destination. In that case, change the AppenderRef tag. It can be used with Console value or some other value (for instance, FrameworkAppender) 
+<br/>
+<br/>
+
+🟢**6. Message format**
+
+If you do not like the format for logging output, you can change it in PatternLayout tag (see log4j2.xml in utbot-framework/src/test/resources/) 
+<br/>
+<br/>
+
+🟢**7. Multiple loggers**
+
+Sometimes it is handy to add an extra logger to a Kotlin class in order to log different functionality independently. 
+
+The primary logger is usually defined as 
+
+`private val logger = KotlinLogging.logger {} `
+
+
+You may add an extra logger 
+
+`private val timeoutLogger = KotlinLogging.logger(logger.name + ".timeout") `
+
+
+Having this logger, you can use it in code with different log levels in parallel with the primary logger.
+<br/>
+<br/>
+
+🟢**7.1 To enable the logger**
+
+1. Go to the file you are currently working on
+2. Select the file in the project tab (alt-f1)
+3. Find the closest log4j2.xml file (usually it is located in the resources file), enable the logger with a desirable log level
+ 
+
+`<Logger name="com.huawei.utbot.engine.UtBotSymbolicEngine.timeout" level="debug"/>`
+
+