Documentation update and set 720p defaults for netflix on RPi

*I'm submitting a ...*
- [ ] bug report
- [x] feature request
- [ ] support request

## General information
Documentation update and set 720p defaults for netflix on RPi

### Prerequisites

* [x] Are you running the latest version?

### Description

Just installed latest OSMC, and added plugin.video.netflix, following instructions here. All went ok but I was unable to view netflix as it was extremely laggy, constantly 'buffering..'.

After checking Youtube worked ok, and looking at the router to see bandwidth I eventually discovered I needed to set Netflix max resolution to 720p, and it all worked!

### Steps to Reproduce

1. Default install of OSMC, and this plugin on RPi3B
2. Try to watch Netflix

**Expected behavior:**

Please update docs with a note on setting max frame rate for RPi's, and ideally have the install script set the rate automatically

**Actual behavior:**

See above

## Context (Environment)
OSMC and RPi3B

### Installation

* [x] I installed the plugin via zip from the Releases page
* [ ] I´m using the Netflix Repo
* [ ] I´m using a different source (Please tell which)

### Operating System

* [ ] Linux (x86/x64)
* [ ] OSX (x86/x64)
* [ ] Windows (x86/x64)
* [x] Linux (ARM)
* [ ] Android

#### Additional information on the environment

[Describe your environment a bit more detailed, are you using LibreElec f.e.]

## Debug log

[Please include a link to your debug log (use something like [http://sprunge.us/](http://sprunge.us/)) or similar, please do not paste]

## Other information

[e.g. detailed explanation, related issues, suggestions how to fix, links for us to have context, etc.]

### Screenshots

[Please add a screenshot if that helps understanding your problem]

[You can erase any parts of this template not applicable to your Issue.]

Review the plugin's installation documentation and install path for Raspberry Pi devices, starting with the instructions referenced in the issue. Confirm how Netflix resolution is configured on an RPi3B, then update the documentation and determine whether the installer can apply a 720p default. Done means the documented setup prevents buffering and the requested default behavior is covered.

Written by the indexing model from the issue text.