Document ft_func with an example

[Flimm]

ft_func and load_ft_func need to be configured together. This commit updates the example to include both settings at once.

I know it's a small change, but it took me quite some time to work this out. So I hope the example configuration will be helpful to others and will save them time.

[L3MON4D3]

Ah, sorry, it's hard to know wherebto omit for brevity and where just that could cost others time😅 Thank you for the change, I appreciate it!

Could you also add a comment that explains that without ft_func there will be no apparent effect on luasnips behaviour? (and squash, so it's one commit+doc-generation)

[L3MON4D3]

Ping If you don't have time, I can do the small modifications as well

[Flimm]

Ping If you don't have time, I can do the small modifications as well

Yes, please! Thank you.