Update IntegrationWithExistingApps.md

[simonbengtsson]

Makes sure a recent version of react native is used by specifying that at least version 0.49 should be used for Android. Otherwise an old 0.20.1 version hosted in jcenter might override the version included from node_modules.

Motivation

Ending up with an ancient version of react native might be confusing to new users trying out react native for the first time.

Test Plan

NA

Release Notes

[DOCS] [MINOR] [IntegrationWithExistingApps.md] - Make sure a node_modules version of react native is used

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[hramos]

Can you tell us a bit more about why such an old version may be used? If we can fix that, it'd be ideal. I don't want to have to update this doc every time we release a new version (0.49 will be considered too old at some point).

[simonbengtsson]

If react native is added after jcenter() in a gradle file it will use a 0.20.1 version hosted by the Facebook organization there. My guess is that jcenter() was used for distribution before npm?

This gradle file would install 0.20.1 of react native:

repositories {
    jcenter() // Included in default android projects
    maven {
        url "$rootDir/../node_modules/react-native/android"
    }
}

But maybe it is a bad idea to mention a specific version even if it has the greater than tag. How about changing the gradle section to this? I.e specifically mentioning jcenter in a comment and moving "..." below the npm react native repository?

allprojects {
    repositories {
        maven {
            // All of React Native (JS, Android binaries) is installed from npm
            url "$rootDir/node_modules/react-native/android"
        }
        ... // Other maven repositories such as `jcenter()` goes here
    }
    ...
}

[hramos]

Thanks for the contribution. The docs have moved to their own repo at facebook/react-native-website. I've applied your change over there.