Update 'README.md'

README.md

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 # deepl-cli
+**deepl-cli** is a command-line utility that uses the **DeepL** API - https://www.deepl.com - a privacy-friendly translation service.
+
+The script is written in **bash** and can run on all UNIX-based systems.
+
+**You need an API key**. You can get it for free from https://www.deepl.com/pro-api.
+## Usage
+```
+./deepl-cli [-h] [-l] target language [-t] text
+```
+For example:
+```
+./deepl-cli -l es -t "Hello World"
+```
+or
+```
+echo "Hello World" |  ./deepl-cli -l es
+> Hola Mundo
+
+```
 
-deepl-cli is a command-line utility that uses the DeepL API - https://www.deepl.com - a privacy-friendly translation service.