Fix `.tmux` output suggesting incorrect target path. (#415)

Fix `.tmux` output suggesting incorrect target path. (#415)

The previous `.tmux` output instructed users to update their TPM run command to `run ~/.local/share/...`, which is typically represented by `XDG_DATA_HOME`. However, the directions also told users to then move the corresponding `.tmux` directory to `XDG_CONFIG_HOME/tmux`.

The two halves of the instructions were conflicting. To resolve this, this commit fixes the second half of the instructions with the correct target path (i.e., `XDG_DATA_HOME`).