README.md: add some basic documentation on how to use pyinvoice

README.md

@@ -1,4 +1,99 @@
-"pyinvoice" is a Python tool to generate PDF invoices using a custom XML format and weasyprint.
+"pyinvoice" is a Python tool to generate PDF invoices using a custom XML format and [WeasyPrint](https://weasyprint.org/).
+
+## Usage
+
+pyinvoice is a command line tool which is really simple to use:
+
+```shell
+$ pyinvoice my-invoice.xml
+```
+
+Afterwards you should find a PDF file `my-invoice.pdf` right next to the xml file.
+Before using pyinvoice for the first time you need to setup/configure some things.
+
+## Installation/Setup
+
+### Installation
+
+TDB
+
+### Create a HTML template for WeasyPrint
+
+TDB
+
+### Create a configuration file
+
+pyinvoice uses a simple configuration file to store information about the invoice issuer.
+That way you can use a single invoice template for different businesses.
+
+If the configuration file is named `invoicing.ini` in the working directory where you called
+pyinvoce the file will be picked up automatically. Otherwise you need to specify the config
+file explicitely using `--config=/path/to/invoicing.ini`.
+
+Example config:
+
+```
+[pyinvoice]
+name      = John Smith
+street    = Main Street 54
+zip       = 80331
+city      = Munich
+tel       = (089) 123456
+email     = [email protected]
+domain    = www.site.example
+
+ustidnr   = DE123456789
+taxnr     = 11/555/00123
+
+bank_iban = DE12 1001 0010 0123 4567 89
+bank_bic  = PBNKDEFF
+bank_name = Postbank
+paypal    = [email protected]
+
+template  = ./templates/invoice.html
+```
+
+Which data you put in there is up to you and the template you use. The only required key is
+`template` which pyinvoice uses to load the right HTML template.
+
+
+---
+
+## Create an Invoice
+
+To create an invoice you need to create an XML file with the right information. pyinvoice will calculate the
+net sum, VAT values and the total sum automatically for you.
+
+```xml
+<?xml version="1.0" encoding='UTF-8'?>
+<invoice invoiceSubject="Software to create PDF Invoices"
+         invoiceDate="21.07.2023" invoiceNumber="00213"
+         defaultVat="0.19">
+
+	<billingAddress>
+	   <name>Customer Ltd</name>
+	   <street>Business Street 2</street>
+	   <zip>10715</zip>
+	   <city>Berlin</city>
+	</billingAddress>
+
+	<item price="230">
+		Development of software to create PDF invoices
+	</item>
+</invoice>
+```
+
+You can use multiple invoice `<item>` elements inside a single invoice. pyinvoice will sum the prices
+for all positions automatically.
+
+
+---
+
+## Advanced Topics
+
+### Custom check functions
+
+TDB
 
 
 ### Item price calculation based on `hours` and `hourly_rate`