Document food budget for event sponsorship (Will-fix: #15206)

wiki/src/contribute/sponsorship_to_attend_events.mdwn

@@ -5,7 +5,7 @@ relevant events such as conferences on behalf of Tails: in most cases
 the project will reimburse the corresponding expenses. Here is how to
 get such sponsorship.
 
-[[!toc levels=2]]
+[[!toc levels=3]]
 
 # General rules
 
@@ -24,6 +24,18 @@ transportation, and conference tickets.
 When spending Tails' money, keep in mind that the project is working
 with a limited budget that is to be used with frugality.
 
+### Food budget
+
+We allocate a budget for food based on the travel cost rate of the German
+Federal Ministry of Finance.
+See the [[calculation below|sponsorship_to_attend_events#food]].
+
+#### Extra food budget
+
+A collective budget of up to 100€ per event is available on top of the
+individual food budgets to eat with important people. Only people from
+tails@boum.org can decide how to use this budget.
+
 ## Is it OK to request sponsorship after the fact?
 
 No, it's not OK. In order to avoid biasing the decision-making process,
@@ -36,8 +48,8 @@ See below for specific deadlines.
 
 Sponsorship requests must include:
 
- - A detailed estimated budget of travel costs, hosting, food, and other
-   expenses.
+ - A detailed estimated budget of travel costs, hosting, and other
+   expenses (like local transportation).
 
  - A list of objectives for the event; in other words, what do you plan
    to do there, and why will it be beneficial for Tails.
@@ -46,6 +58,40 @@ Sponsorship requests must include:
    example, "getting to know many other Tails people in person" is
    often a valid objective.
 
+   <a id="food"></a>
+
+ - The number of lunches and dinners that you will have to pay yourself,
+   including during travel.
+
+   We will calculate your food budget using the following formula:
+
+       ( number of lunches + dinners ) × factor × official German rate
+
+   - *factor* is:
+
+     - 0.3 outside of Germany
+     - 0.4 in Germany
+
+   - The *official German rate* can be found by searching online for
+     "*Steuerliche Behandlung von Reisekosten und Reisekos­tenvergütungen*" for
+     the current year.
+
+     For example: *[site:bundesfinanzministerium.de Steuerliche Behandlung von
+     Reisekosten und Reisekos­tenvergütungen
+     2018](https://duckduckgo.com/?q=site%3Abundesfinanzministerium.de+Steuerliche+Behandlung+von+Reisekosten+und+Reisekos%C2%ADtenverg%C3%BCtungen+2018)*.
+
+     In the PDF, refer to the "*Pauschbeträge für Verpflegungsmehraufwendungen
+     bei einer Abwesenheitsdauer von mindestens 24 Stunden je Kalendertag*"
+     (first column).
+
+   For example, if you are traveling to London for 3 days and eat 2 meals
+   during your travel, your food budget will be:
+
+       ( ( 1 lunch + 1 dinner ) × 3 days + 2 meals ) × 0.3 × 62€ = 148.80€
+
+   Your food budget is the maximum that you can spend on food but you will have
+   to justify your *exact expenses* when reporting about your travel.
+
 ## Who should I write to?
 
 Send your sponsorship request to the <tails@boum.org> private mailing