Document voices in English for other regions

[HadrienGardeur]

The current list of recommended voices for English has almost 80 voices already, but it only covers the following regions:

• United States (en-us)
• United Kingdom (en-gb)
• Canada (en-CA)

Additional voices are also available for the following regions:

• Australia (en-au)
• Hong Kong (en-hk)
• India (en-in)
• Ireland (en-ie)
• Kenya (en-ke)
• New Zealand (en-nz)
• Nigeria (en-ng)
• Scotland (en-gb-u-sd-gbsct)
• Singapore (en-sg)
• South Africa (en-za)
• Tanzania (en-tz)

Given the large number of regions covered by English, prioritizing these languages might be a challenge.