Enhance Pinned Query documentation

[SerethiX]

The documentation currently lacks the information, that sorting makes the query useless: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-pinned-query.html

The information can be found by googling a bit, but this should be part of the official documentation: https://www.elastic.co/de/blog/using-elasticsearch-pinned-queries-to-promote-specific-results

[elasticsearchmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

Pinging @elastic/search-eng (Team:SearchOrg)

[elasticsearchmachine]

Pinging @elastic/search-relevance (Team:Search - Relevance)