is_local parameter on set_config function

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.5/config-setting.html
Description:

Hello,

I have just used the set_config(...) function for the first time and it took
me a bit of experimenting to understand the effect of the is_local
parameter. My suggestion would be to add a bit of explanation on that.

Thank you
Joao