[DOC-REVIEW] README update (PR #1402)

[Sharon-iguazio]

Doc-review edits for README.md changes done by Yaron H. in PR #1402

[Sharon-iguazio]

@yaronha

1. Please review and approve by doc changes in this PR.

2. As part of the README changes in PR update readme #1402, you also replaced "dealer" references with "scaler" and removed the "Data bindings" section. However, the repo still has instances of the "dealer" and "data bindings", including in the docs and CLI text (see grep results below). If we want to change the terminology, it should be consistent. I can replace "dealer" instances with "scalar", if you wish, but I don't know what to do about the data-binding references.

   git grep -nli "dealer"
   ROADMAP.md
   docs/concepts/architecture.md
   pkg/functionconfig/types.go
   vendor/github.com/sergi/go-diff/testdata/speedtest1.txt
   vendor/golang.org/x/net/publicsuffix/table.go
   vendor/golang.org/x/net/publicsuffix/table_test.go

   $ git grep -li "data.binding"
   ROADMAP.md
   cmd/playground/static/assets/app.js
   cmd/playground/static/index.html
   docs/concepts/architecture.md
   docs/reference/function-configuration/function-configuration-reference.md
   docs/reference/nuctl/nuctl_deploy.md
   docs/tasks/deploying-functions.md
   pkg/nuctl/command/deploy.go
   pkg/nuctl/command/update.go
   pkg/processor/databinding/databinding.go
   pkg/processor/databinding/v3io/databinding.go
   pkg/processor/runtime/pypy/nuclio_interface.py
   pkg/processor/runtime/runtime.go
   pkg/processor/util/v3io/v3ioutil.go

[Sharon-iguazio]

@omesser @eran-nussbaum as part of my review for this PR, I noticed that the ROADMAP.md doc hasn't been updated since Aug 2018. => Please either update this file or remove it (and all references to it).

[Sharon-iguazio]

UPDATE: According to Eran, (1) "scalar" is a new concept; it doesn't replace "dealer", which never really materialized. (2) "data binding" is still supported in the code but we want to gradually retire it. => We'll discuss offline removing/replacing the related references to the removed terminology.