Added README.md, example PDF and screenshot.

README.md

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+# Bilingual Invoice Generator
+
+![Example invoice screenshot](example/invoice_example_screenshot.png)
+
+[PDF](example/invoice_1_01_02_20.pdf)
+
+## Build
+
+### Install dependencies
+
+```shell
+composer install
+```
+
+### Create config and translation files
+
+```shell
+cp config/parameters.yaml.dist config/parameters.yaml.dist
+cp translations/source.yaml.dist translations/source.yaml
+cp translations/target.yaml.dist translations/target.yaml
+```
+
+## Usage
+
+```shell
+# Generate file name
+./generate 123 ./
+
+# Use exact file name
+./generate 123 ./invoice.pdf
+
+# Set issue date
+./generate 123 ./ --issue-date 01.01.1970
+
+# Get help
+./generate --help
+```