docs: jsonalchemy grammar and rewording
docs: jsonalchemy grammar and rewording

* Rewords sentences that were incomprehensible or hard to understand
  and splits long chunks of information into bullet points.

* Changes informal pronouns to formal.

* Fixes a triple-quote.

Signed-off-by: Dimitrios Semitsoglou-Tsiapos <6a6862363aaa6e93bbf0fa721048d2ca97773c19@cern.ch>

inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio