Add note about node >14 in gulp.watch documentation

Describe your idea for a new feature

Just add a small warning here https://gulpjs.com/docs/en/getting-started/watching-files about NodeJS version about Gulp not supporting NodeJS >= 14 for watching files.

Explain the problem your idea is trying to solve

I have multiple co-workers wanting to use this gulp feature and they are all missing the fact that this is not compatible with current LTS versions of NodeJS. So it could help to prevent users that this feature is not available for recent versions of NodeJS.

How will it benefit gulp and its users?

I think it will help users to not have to search in closed issues or discussions to have this information. I think this is reasonable since Gulp seems not going to be updated soon.