Use dockerignore instead of "rm -rf .git"

This reduces the number of layers in the dockerfile by one

.dockerignore

@@ -0,0 +1 @@
+.git/

Dockerfile

@@ -11,8 +11,6 @@ COPY . /botamusique
 
 WORKDIR /botamusique
 
-RUN rm -rf .git*
-
 RUN python3 -m venv venv && \
     venv/bin/pip install wheel && \
     venv/bin/pip install -r requirements.txt