Mention the limitations of slot naming with v-slot directive

[NataliaTepluhina]

v-slot directive currently does not support slot names that

• start with the square bracket (because that's how we define the dynamic slot name);
• have whitespace;
• have special characters used by directive attributes: i.e. . in a scoped slot name, as it will instruct Vue to treat it as a directive modifier

This should be mentioned in slots documentation as slot naming limitations.

Related discussion can be found here

[rabbitwerks]

is this still relevant to update the docs? currently the docs show using the v-slot:[dynamicName] as being the correct syntax, where as the issue attached demonstrates that the first character cannot be a space or [.
is this issue resolved with Vue now or are the docs needing to be updated?