DOCS: IMDG Reference Manual: Minor improvement propositions for intro page - Editions chapter

https://github.com/hazelcast/imdg-docs/blob/master/docs/modules/ROOT/pages/index.adoc

1. Hazelcast or Hazelcast IMDG - > usually, such editions are called “Community edition”
2. Hazelcast is also the name of the company (Hazelcast, Inc.) providing the Hazelcast product. - > I would propose to move it to “References” or somewhere else, since this is a chapter for “Editions”, not terms
3. Hazelcast or Hazelcast IMDG refers to the open - > It seems, it would be better (since we are describing editions, not terms) to “Hazelcast IDMG (Hazelcast) is an open…”
4. Pro and Enterprise contains particular features description, but first edition - not. I think, it would be better to describe main functionality for the fist edition, and further just expand the list.
5. The Pro and Enterprise editions offer all the features of the open source edition - > this should be removed if “4” is processed
6. This is restricted to 3 members on the freely available but unlicensed version of Management Center -> It seems to me, it have to be in the first edition like “MC support for 3 members” and then, for Pro - “MC - unlimited”
7. Not all differences are highlighted, see, for example, Pivotal Cloud Foundry, thus, it seems, it would be nice to mention that only main features are listed here. I propose to add this link https://hazelcast.com/product-features/imdg-comparison/ for details