feat: add example bill

bill.example.yaml

@@ -0,0 +1,49 @@
+subject: Web development of a super cool app
+date: 2022-02-29
+# your internal bill id
+id: '2022-02-1'
+
+provider: # you (the freelancer)
+    name: John Doe
+    address:
+        - first address line
+        - 89767 City name
+    mobile: '+2395499541'
+    mobile_formatted: '+23 95 49 95 41' # TODO: add auto formatting
+    email: johndoe@example.org
+    siret: XXXXXXX
+    tax_id: FRXXXXX
+    naf: 6201Z
+
+customer:
+    name: My super customer
+    address:
+        - blabla bla
+        - 92404 Wow City
+    siret: XXXX
+    tax_id: FRXXX
+    contact:
+        name: Alice
+        email: alice@another-company.com
+
+daily_rate: 300
+currency: EUR
+
+categories:
+    - name: The magnificient blog of your super website
+      tasks:
+          - name: "Manage articles"
+            days: 1.5
+          - name: "RSS feed"
+            days: 0.5
+          - name: "Beautiful reader"
+            days: 0.5
+          - name: "External connexion"
+            days: 0.9
+    - name: Deployment to production
+      tasks:
+          - name: "Install a web server"
+            days: 0.3
+          - name: "Deployment of the app"
+            days: 0.5
+