Add changes to v6 page

Co-authored-by: Calvin Lau <calvin.lau@digital.cabinet-office.gov.uk>

Co-authored-by: seaemsi <50173207+seaemsi@users.noreply.github.com>

Author: 2 people

source/changes-to-govuk-frontend-v6/index.html.md.erb

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+---
+title: Changes in GOV.UK Frontend v6.0.0
+weight: 95
+---
+
+# Changes in GOV.UK Frontend v6.0.0
+
+GOV.UK Frontend v6.0.0 includes changes to:
+
+- improve our Sass architecture
+- use an updated type scale to improve accessibility for small screens
+- update colours to use the GOV.UK web palette in the GOV.UK brand guidelines
+- improve the page template layout
+
+We’ve also removed a number of deprecated APIs, Sass variables and component options.
+
+## Migrating from v5 to v6.0.0
+
+Follow the guidance about [staying up to date with GOV.UK Frontend](https://frontend.design-system.service.gov.uk/staying-up-to-date/).
+
+When making the decision to migrate, consider your service’s requirements and your ability to update Sass tooling and templates. In particular, you must update to [Dart Sass v1.79.0 or later](https://sass-lang.com/dart-sass/) before upgrading to v6.0.0.
+
+## Benefits of updating to v6.0.0
+
+By updating to v6.0.0 you’ll:
+
+- stay aligned with the GOV.UK look and feel: we’ve updated GOV.UK Frontend to use the GOV.UK web palette from the GOV.UK brand guidelines
+- benefit from a more consistent colour system in certain components
+- get the latest accessibility improvements, based on ongoing testing and feedback from services across government
+- benefit from a smaller CSS payload
+- be able to customise the page template further than before
+
+## Updating to v6.0.0
+
+Read the [GOV.UK Frontend v6.0.0 release notes](https://github.com/alphagov/govuk-frontend/releases/v6.0.0) to see the full list of breaking and recommended changes.
+
+You might need to update some items to update to v6.0.0, including:
+
+- updating your Sass compiler to [Dart Sass v1.79.0 or later](https://sass-lang.com/dart-sass/)
+- using the latest GOV.UK web palette 
+- using the new colour functions and replacing colours to follow the new naming convention
+
+You'll need to check some items still work as expected, including:
+
+- making sure any custom use of functional colours still follows best accessibility practice for contrast and legibility
+- updating any custom header or footer content, as we've changed how you can use and customise these components
+- testing the new type scale in your service to see if you need to make any adjustments
+
+You’ll also need to remove references to any APIs, Sass variables and component options that we’ve removed.