Added JavaScript installation guide

docs/JavaScriptSupport.md

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+# UnitTestBot JavaScript plugin setup
+
+## How to start using UnitTestBot JavaScript
+
+1. [Install](https://www.jetbrains.com/idea/download/) the latest version of IntelliJ IDEA Ultimate.
+2. [Install](https://plugins.jetbrains.com/plugin/19445-unittestbot) the latest version of UnitTestBot plugin.
+3. [Install](https://nodejs.org/en/download/) Node.js 10.0.0 or later. Add Node.js to environment variables for better experience.
+4. In your IntelliJ IDEA, go to **File** > **Settings** > **Tools** > **UnitTestBot** and enable **Experimental languages support**.
+5. Go to **File** > **Settings** > **Languages & Frameworks**, choose **Node.js** and check if the path to Node.js executable file is specified.
+6. In a JavaScript file, press **Alt+Shift+U** to open the generation dialog.
+
+## Troubleshooting: _npm_ cannot install requirements
+
+1. The system prohibits installation
+
+Solution: run _cmd_ via `sudo` or with administrator access, run `npm install -g <missing requirement>`.
+
+2. Node.js is missing, or _npm_ is not installed
+
+Solution: install Node.js with default configuration from the official website.
+
+# JavaScript Command Line Interface usage
+
+## Build
+
+JAR file can be built in [GitHub Actions](https://github.com/UnitTestBot/UTBotJava/actions/workflows/publish-plugin-and-cli-from-branch.yml) with the `publish-plugin-and-cli-from-branch` script.
+
+## Requirements
+
+* [Install](https://nodejs.org/en/download/) Node.js 10.0.0 or later
+* [Install](https://www.oracle.com/java/technologies/downloads/) Java 11 or later
+* Install _nyc_ 15.1.0 or later: `> npm install -g nyc`
+* Install Mocha 10.0.0 or later: `> npm install -g mocha`
+
+## Basic usage
+
+### Generate tests: `generate_js`
+
+    java -jar utbot-cli.jar generate_js --source="dir/file_with_sources.js" --output="dir/generated_tests.js"
+
+  This will generate tests for top-level functions from `file_with_sources.js`.
+
+#### Options
+
+- `-s, --source <path>`
+
+  _(required)_ Source code file for test generation.
+- `-c, --class <classname>`
+
+  Specifies the class to generate tests for.
+  If not specified, tests for top-level functions or a single class are generated.
+
+- `-o, --output <dir/filename>`
+
+  File for generated tests.
+- `-p, --print-test`
+
+  Specifies whether a test should be printed out to `StdOut` (default = false).
+- `-t, --timeout <seconds>`
+
+  Timeout for a single test case to generate: in seconds (default = 15).
+- `--coverage-mode <BASIC/FAST>`
+
+  Specifies the coverage mode for test generation (used for coverage-based optimization). For now, the fast mode cannot deal with exceeding timeouts, but works faster (default = FAST). Do not use the fast mode if you guess there might be infinite loops in your code.
+- `--path-to-node <path>`
+
+  Sets a path to Node.js executable (default = "node").
+- `--path-to-nyc <path>`
+
+  Sets a path to _nyc_ executable (default = "nyc").
+- `--path-to-npm <path>`
+
+  Sets a path to _npm_ executable (default = "npm").
+
+### Run generated tests: `run_js`
+
+    java -jar utbot-cli.jar run_js --fileOrDir="generated_tests.js"
+
+  This will run generated tests from a file or directory.
+
+#### Options
+
+- `-f, --fileOrDir`
+
+  _(required)_ File or directory with tests.
+- `-o, --output`
+
+  Specifies the output TXT file for a test framework result (if empty, prints the result to `StdOut`).
+
+- `-t, --test-framework <name>`
+
+  Test framework to use for test running (default = "Mocha").
+
+### Generate a coverage report: `coverage_js`
+
+    java -jar utbot-cli.jar coverage_js --source=dir/generated_tests.js
+
+  This will generate a coverage report for generated tests and print it to `StdOut`.
+
+#### Options
+
+- `-s, --source <file>`
+
+  _(required)_ File with tests to generate a report for.
+
+- `-o, --output`
+
+  Specifies the output JSON file for a coverage report (if empty, prints the report to `StdOut`).
+- `--path-to-nyc <path>`
+
+  Sets a path to _nyc_ executable (default = "nyc").