jest-preset-default: update README to reflect current status

[jsnajdr]

Updates the jest-preset-default README, namely the list of Jest options the preset sets. This documentation hasn't changed much since the preset was originally created in 4466f21, but the options we're setting today are different.

• removes the mention of verbose, snapshotSerializers and timers options
• adds description of the testPathIgnorePatterns option
• improves the description of how we set the testMatch option

[gziolo]

Thank you so much for bringing this section up to date 💯

[tyxla]

Thanks Jarda! 🚀