Add other API functions to README

Author: codesalatdev

README.md

@@ -28,12 +28,73 @@ picnic = PicnicAPI(username='username', password='password', country_code="NL")
 
 The country_code parameter defaults to `NL`, but you have to change it if you live in a different country than the Netherlands (ISO 3166-1 Alpha-2). This obviously only works for countries that picnic services.
 
-## Searching for a product
+## Searching for an article
 
 ```python
 picnic.search('coffee')
 ```
 
 ```python
 [{'items': [{'id': 's1019822', 'name': 'Lavazza Caffè Crema e Aroma Bohnen', 'decorators': [], 'display_price': 1799, 'image_id': 'aecbf7d3b018025ec78daf5a1099b6842a860a2e3faeceec777c13d708ce442c', 'max_count': 99, 'unit_quantity': '1kg', 'sole_article_id': None}, ... ]}]
+```
+
+## Get article by ID
+
+```python
+picnic.get_article("s1019822")
+```
+```python
+{'name': 'Lavazza Caffè Crema e Aroma Bohnen', 'id': 's1019822'}
+```
+
+## Get article by GTIN (EAN)
+```python
+picnic.get_article_by_gtin("8000070025400")
+```
+```python
+{'name': 'Lavazza Caffè Crema e Aroma Bohnen', 'id': 's1019822'}
+```
+
+## Check cart
+
+```python
+picnic.get_cart()
+```
+
+```python
+{'type': 'ORDER', 'id': 'shopping_cart', 'items': [{'type': 'ORDER_LINE', 'id': '1470', 'items': [{'type': 'ORDER_ARTICLE', 'id': 's1019822', 'name': 'Lavazza Caffè Crema e Aroma Bohnen',...
+```
+
+## Manipulating your cart
+All of these methods will return the shopping cart.
+
+```python
+# Add product with ID "s1019822" 2x
+picnic.add_product("s1019822", 2)
+
+# Remove product with ID "s1019822" 1x
+picnic.remove_product("s1019822")
+
+# Clear your cart
+picnic.clear_cart()
+```
+
+## See upcoming deliveries
+
+```python
+picnic.get_current_deliveries()
+```
+
+```python
+[{'delivery_id': 'XXYYZZ', 'creation_time': '2025-04-28T08:08:41.666+02:00', 'slot': {'slot_id': 'XXYYZZ', 'hub_id': '...
+```
+
+## See available delivery slots
+
+```python
+picnic.get_delivery_slots()
+```
+
+```python
+{'delivery_slots': [{'slot_id': 'XXYYZZ', 'hub_id': 'YYY', 'fc_id': 'FCX', 'window_start': '2025-04-29T17:15:00.000+02:00', 'window_end': '2025-04-29T19:15:00.000+02:00'...
 ```