chore: fix mount directory names in README

[Erisa]

For both user and root services, the correct base directory is /mnt/tigris/:

tigrisfs/pkg/[email protected]

Lines 10 to 11 in b4a26b5

	ExecStartPre=/bin/mkdir -p ${MOUNT_PREFIX}/mnt/tigris/%i
	ExecStart=/usr/bin/tigrisfs $OPTS %i ${MOUNT_PREFIX}/mnt/tigris/%i

tigrisfs/pkg/[email protected]

Lines 10 to 11 in b4a26b5

	ExecStartPre=/bin/mkdir -p ${MOUNT_PREFIX}/mnt/tigris/%i
	ExecStart=/usr/bin/tigrisfs $OPTS %i ${MOUNT_PREFIX}/mnt/tigris/%i

[Copilot]

Pull Request Overview

This PR updates the documentation in the README to reflect the correct base mount directory for both user and root services, ensuring consistency with the service configuration.

• Update mount directory path from tigrisfs to tigris in user service instructions
• Update mount directory path from tigrisfs to tigris in root service instructions

[ovaistariq]

Thanks for the contribution