Usually in your shell profile as mine is in my .bashrc
# RClone Config file
RCLONE_CONFIG=/data/rclone/rclone.conf
export RCLONE_CONFIG
In Systemd, it is like this:
cat gmedia-rclone.service
[Unit]
Description=RClone Service
PartOf=gmedia.service
RequiresMountsFor=/data
# This uses cmount as it's a built version of rclone from source
# sync_read must be used or files are read out of order
# auto_cache allows for system memory to be used
[Service]
Type=notify
Environment=RCLONE_CONFIG=/data/rclone/rclone.conf
ExecStart=/usr/bin/rclone mount gcrypt: /GD \
--allow-other \
--bind 192.168.1.30 \
--buffer-size 1G \
--dir-cache-time 72h \
--fast-list \
--log-level INFO \
--log-file /home/felix/logs/rclone.log \
--umask 002 \
--vfs-read-chunk-size 128M \
--vfs-read-chunk-size-limit off
ExecStop=/bin/fusermount -uz /GD
Restart=on-failure
User=felix
Group=felix
[Install]
WantedBy=gmedia.service