[DOC-REVIEW] Frames README & help text (#3): Overview, user-auth, Cli…

…ent constructor, Create, and Write params doc imprv; misc cosmetics (#306)

* [DOC Frames README & help text: Minor text edits

* [DOC] Frames README: minor user-authentication edits

* [DOC] Frames README: add a client-constructor @token example

* [DOC] Frames README: minor edits to the common Client method params doc

* [DOC] Frames README: Edit the create method doc

* [DOC] Frames help text: Edit the __init__ (constructor) & create method doc

* [DOC] Frames README: Cosmetic changes, including examples sections restructure

* [DOC] Frames help text: Clien constructor doc edits; doc data_url param externally

* [DOC] Frames README: Edit the `rate` param description for tsdb create

* [DOC] Frames README: Edit the `rate` param description for tsdb create (#2)

* [DOC] Frames README: (Cosmetics) Pleace `kv` sections before `tsdb` sections

* [DOC] Frames help text: (Minor) Unify backend-specific params section prefix & platform doc refs

* [DOC] Frames README: Overview - move Backend Types before Client Methods

* [DOC] Frames README (Minor): "backend" params valid values - "csv" last

* [DOC] Frames README: (Cosmetics) Single > double quotation marks (for consistency)

* [DOC] Frames README: Client constructor - remove "user" param from access-key ("token") example

* [DOC] Frames help text: Edit `create` syntax & `attrs` param requirement

* [DOC] Frames help text: `write` - edit `dfs` & `labels` params doc

* [DOC] Frames README (Minor): Add examples for `stream` `create` param values

* [DOC] Frames help text: `write` - edit `dfs` & `labels` params doc for the "tsdb" backend

* [DOC] Frames README: Fix param name (`username` > `user`)

* [DOC] Frames README: (Minor cosmetics) Replace a colon with a period