docs(info): add all mathematical functions in readme

README.md

@@ -8,6 +8,16 @@ Bot for the private server Discord "Les Copaings"
 - Roles management
 - Purge command
 
+### XP
+
+Functions:
+- $xp_message(x;y) = \frac{0.025 x^{1.25}}{y^{-0.5}}+1$ where $x$ is the length of the message and $y$ is the diversity of the 
+message (number of different rune)
+- $xp_vocal(x)=0.01 x^{1.3}+1$ where $x$ is the time spent in vocal
+- $level(x)=0.2 x^{0.5}$ where $x$ is the xp
+- $level^{-1}(x)=(5x)^2$ where $x$ is the level
+- $lose(x,y)= 10^{-2+\ln(x/85)}x^2+\lfloor y/100 \rfloor$ where $x$ is the inactivity time (hour) and $y$ is the xp
+
 ## Technologies
 
 - Go 1.22