docs(entity): updated FAQ url for Redux docs

[sanket-work]

https://redux.js.org/faq/organizing-state#can-i-put-functions-promises-or-other-non-serializable-items-in-my-store-state

PR Checklist

Please check if your PR fulfills the following requirements:

• [ x] The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• [ x] Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[ngrxbot]

Preview docs changes for 876db88 at https://previews.ngrx.io/pr2297-876db88/

[brandonroberts]

Thanks @sanketCactus!