chore: adjust run instruction based on the user platform

[Simek]

Summary:

This PR adjust the run instructions printed at the end of init command run which now should show only valid targets for the user platform. I have also updated the links for the desktop forks from MS to lead exactly to platform specific guides.

• iOS and macOS instructions will be only visible on darwin
• Windows instructions will be only visible on win32

Test Plan:

I was trying to test the init locally using Contributing guide, but I have experienced problems and issues after publishing react-native master locally.

One of many problems which leads to init termination:

error Couldn't find package "@typescript-eslint/experimental-utils@2.34.0" required by "@typescript-eslint/eslint-plugin@^2.25.0" on the "npm" registry.
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
Error: Couldn't find package "eslint-plugin-flowtype@2.50.3" required by "@react-native-community/eslint-config@^1.1.0" on the "npm" registry.
    at MessageError.ExtendableBuiltin (/usr/local/Cellar/yarn/1.22.5/libexec/lib/cli.js:721:66)
    at new MessageError (/usr/local/Cellar/yarn/1.22.5/libexec/lib/cli.js:750:123)
    at PackageRequest.<anonymous> (/usr/local/Cellar/yarn/1.22.5/libexec/lib/cli.js:36539:17)
    at Generator.throw (<anonymous>)
    at step (/usr/local/Cellar/yarn/1.22.5/libexec/lib/cli.js:310:30)
    at /usr/local/Cellar/yarn/1.22.5/libexec/lib/cli.js:323:13
    at processTicksAndRejections (internal/process/task_queues.js:93:5)

Please let me know is there any other way to test the init command without publishing react-native locally.

[Simek]

CI fail looks unrelated to the changes performed within this PR (similar issue happen in #1280 (comment)):

• https://dev.azure.com/react-native-community/cli/_build/results?buildId=1509&view=logs&j=12f1170f-54f2-53f3-20dd-22fc7dff55f9&t=bd05475d-acb5-5619-3ccb-c46842dbc997&l=32

[thymikee]

Mind sending some screenshots on how the end result looks now (at least on one platform)?

[Simek]

Preview

@thymikee It looks like I had to remove one indentation from the nested in conditionals instructions:

[thymikee]

Let's address this then

[Simek]

Preview after whitespace changes (macOS)

[Simek]

Windows preview

[Simek]

@asklar Is it possible to create the short URLs for both platforms, leading to Getting Started pages?

For example:

• Windows: https://aka.ms/ReactNativeWin, ReactNativeGuideWindows (ReactNativeWindows is taken by the GitHub repository)
• macOS: https://aka.ms/ReactNativeMacOS, ReactNativeGuideMacOS

[asklar]

@Simek I've created ReactNativeMacOS, ReactNativeGuideWindows and ReactNativeGuideMacOS

[Simek]

@thymikee I have changed the color of Windows instructions header to cyan to avoid the black font issue in PS on Windows. macOS header can still use magenta, because there are no issues with rendering this color in Terminal.

[thymikee]

Thank you @Simek 🚀 !