Fix accessibility testing to include slow internet connection

[kelliedesigner]

Accessibility testing page is missing guidance on testing for the slow internet connection.

[kelliedesigner]

Key findings from Ofcom:

• a little under half of the country still use the much slower and less reliable ADSL based pure copper lines

• Wales suffers for much slower internet speeds than England.

• A large gap in speeds between urban and rural areas persists.

• Network congestion, poor home wiring, faults and traffic management measures can also have an impact on internet speed.

• not everyone can afford, is aware of, or feels the need to upgrade a faster connection, even when one may be available.

• there are still remote rural communities and digitally disadvantaged urban pockets who don't have better options available.

• the government's new Universal Service Obligation (USO) promises to set a minimum download speed of at least 10Mbps for all by 2020.

• 2% of the UK's population (11% of the UK's rural population) has a speed of 2MBPS or less

• ADSL network speeds can be as slow as 3.8MBPS

[kelliedesigner]

Closing as Lighthouse includes latency checks