Change execution schedule (#5)

**README**
- Changed `CRON_TIME` in `docker-compose`.
- Added info on when the script runs.

**Dockerfile**
- Changed execution schedule from 5am everyday to every 12 hours.

Dockerfile

@@ -9,7 +9,7 @@ RUN apk add --no-cache \
     zip \
     tzdata
 
-ENV CRON_TIME "0 5 * * *"
+ENV CRON_TIME "* */12 * * *"
 ENV UID 100
 ENV GID 100
 ENV CRONFILE /etc/crontabs/root