feat: Update readme with theme description (#415)

# [DCMAW-18949](https://govukverify.atlassian.net/browse/DCMAW-18949):
Update README to align with design systems

- Update readme with theme description

## Evidence of the change

[//]: # (Screenshots / uploaded videos go here)

## Checklist

### Before creating the pull request

- [x] Commit messages that conform to conventional commit messages.
- [x] Ran the app locally ensuring it builds.
- [x] Tests pass locally.
- [x] Pull request has a clear title with a short description about the
feature or update.
- [ ] Created a `draft` pull request if it's not ready for review.

### Before the CODEOWNERS review the pull request

- [x] Complete all Acceptance Criteria within Jira ticket.
- [x] Self-review code.
- [x] Successfully run changes on a testing device.
- [x] Complete automated Testing:
  * [ ] Unit Tests.
  * [ ] Integration Tests.
  * [ ] Instrumentation / Emulator Tests.
- [x] Review [Accessibility considerations].
- [ ] Handle PR comments.

### Before merging the pull request

- [ ] [Sonar cloud report] passes inspections for your PR.
- [ ] Resolve all comments.

[Sonar cloud report]:
https://sonarcloud.io/project/overview?id=di-mobile-android-ui
[Accessibility considerations]:
https://developer.android.com/guide/topics/ui/accessibility/testing


[DCMAW-18949]:
https://govukverify.atlassian.net/browse/DCMAW-18949?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: chrisdondigital

README.md

@@ -7,12 +7,17 @@ Libraries to provide some useful and generic UI components, pages and themes to
 
 ### Theme
 
-This library contains the `GdsTheme`, collecting the colour schemes, fonts/typography and some useful dimensions.
+This library contains:
+- The `GdsTheme`
+- Pre-defined colour objects in line with the GDS Design System
+- Day and night mode colour schemes
+- Typography text styles
+- Commonly used dimensions.
 
 ### Components 
 
 This library contains 'building blocks', smaller, reusable components - the only new components to be created should have full specs provided by the user centred design (UCD) team.
-All new components should be created in `componentsv2` module - `components` module will be deprecated and removed once all dependencies from other repositories have been removed. 
+All new components should be created in `componentsv2` module
 
 Components include:
 
@@ -35,11 +40,12 @@ Components include:
 - GdsTopAppBar
 - GdsWarningText
 - GdsCard
+- CameraContent (componentsv2-camera submodule)
 
 ### Patterns
 
 This library contains page patterns to help with the creation of similar styles of page. They use components from the `componentsv2` library to build larger patterns.
-All new components should be created in `patterns` module - `pages` module will be deprecated and removed once all dependencies from other repositories have been removed.
+All new components should be created in `patterns` module
 
 Patterns include:
 
@@ -49,6 +55,7 @@ Patterns include:
 - ErrorScreen
 - LeftAlignedScreen
 - LoadingScreen
+- QrScannerScreen (patterns-camera submodule)
 
 ## Installation