📙 Add text search across multiple fields

[mtrezza]

Link to section:
https://docs.parseplatform.org/js/guide/#queries-on-string-values

What is the issue?
Should contain instruction for a text search across multiple fields, see parse-community/parse-server#6781 (comment).

Can you propose a solution?
Add description from parse-community/parse-server#6781 (comment).