Dockerfile with better caching

thanks @divadsn

Dockerfile

@@ -3,6 +3,9 @@ FROM python:alpine
 RUN apk add --no-cache gettext
 
 WORKDIR /app/
+COPY requirements.txt .
+RUN pip install -r requirements.txt
+
 COPY . .
 
 RUN cd locales && find . -maxdepth 2 -type d -name 'LC_MESSAGES' -exec ash -c 'msgfmt {}/unobot.po -o {}/unobot.mo' \;