docs: add link to #72 describing solution

[jedrzejboczar]

Adds a note about solution to #72.

[jedrzejboczar]

@josh-nz Does it look ok?

[josh-nz]

You have mentioned the important parts:

1. cwd can be overwritten
2. provided a link to the issue so users can find more detail if needed.

I probably would explain it a little more:

When `autosave.cwd` is set to `true`, there are situations were the cwd session might be saved when it is not wanted. Two such situations are when file arguments are passed to Neovim, and when a session is closed via `:PossessionClose`. More details can be found in [this issue](https://github.com/jedrzejboczar/possession.nvim/issues/72). To prevent overwriting the cwd session in these cases, you can use the following setting:

Adding a note to the docs was a good idea. 👍