[Chore] Add Codecov and update readme

[luongvo]

What happened 👀

• Integrate CodeCov for CI workflow to show code coverage in PR & README.
• Add exclude rules for Kover.
• Update README.

Insight 📝

There is an issue with CodeCov that it does not show code coverage correctly for Kotlin Multiplatform yet

• Codecov can't understand Multiplatform + Multi-module Kotlin/kotlinx-kover#189
• Integrate with codecov.io Kotlin/kotlinx-kover#16.

Proof Of Work 📹

• CodeCov https://app.codecov.io/gh/luongvo/kmm-survey.
• Please check README.

[github-actions]

	15 Warnings
⚠️	Uh oh! Your project is under 80% coverage!
⚠️	android/src/main/java/vn/luongvo/kmm/survey/android/ui/common/Toaster.kt#L14 - Toast created but not shown: did you forget to call show() ?
⚠️	android/src/main/java/vn/luongvo/kmm/survey/android/ui/screens/login/LoginScreen.kt#L35 - Function parameter viewModel is unused.
⚠️	android/src/main/java/vn/luongvo/kmm/survey/android/ui/screens/login/LoginScreen.kt#L57 - The function LoginScreenContent is too long (70). The maximum length is 60.
⚠️	android/src/main/res/drawable/bg_login.jpg#L0 - Found bitmap drawable res/drawable/bg_login.jpg in densityless folder
⚠️	android/src/main/res/mipmap-hdpi/ic_launcher_round.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/main/res/mipmap-ldpi/ic_launcher.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/main/res/mipmap-mdpi/ic_launcher.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/main/res/mipmap-mdpi/ic_launcher_round.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/main/res/mipmap-xxxhdpi/ic_launcher_round.png#L0 - Launcher icon used as round icon did not have a circular shape
⚠️	android/src/staging/res/mipmap-hdpi/ic_launcher_round.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/staging/res/mipmap-ldpi/ic_launcher.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/staging/res/mipmap-mdpi/ic_launcher.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/staging/res/mipmap-mdpi/ic_launcher_round.png#L0 - Launcher icons should not fill every pixel of their square region; see the design guide for details
⚠️	android/src/staging/res/mipmap-xxxhdpi/ic_launcher_round.png#L0 - Launcher icon used as round icon did not have a circular shape

🧛 build Code Coverage: 5.28%

Coverage of Modified Files:

File	Coverage

Modified Files Not Found In Coverage Report:

README.md
build.gradle.kts
build.gradle.kts
review_pull_request.yml

Codebase cunningly covered by count Shroud 🧛

Generated by 🚫 Danger

[luongvo]

This's a small chore so I will merge this with 1 approval, please don't hesitate to put a comment even after merging.