[splash] create splash screen black screen fyi (expo#33)

black-screen-before-splash.md

@@ -0,0 +1,24 @@
+# Why does my app launch with a black screen on iOS?
+
+Sometimes you might encounter a black screen before your launch screen on iOS. While this can be annoying, it usually boils down to a few possible issues that are easy to debug and resolve! 
+
+**Note:** The easiest way to set up your splash screen is to use the `@expo/configure-splash-screen` package like so: 
+```bash
+yarn expo-splash-screen -p ios -i splash.png -b "#ffffff"
+```
+
+### 1. Your device or simulator is caching the previously configured splash screen
+
+If you've manually added your own splash image to `Images.xcassets`, then you might need to restart your simulator or device. 
+
+### 2. The provided asset may be invalid
+
+If you never see your splash screen image i.e the app launch transitions from black screen to your app, then there might be a problem with your image.
+
+This could be a number of different issues, [this StackOverflow thread](https://stackoverflow.com/questions/63978396/launch-screen-not-working-on-ios-14-with-xcode-12) outlines a number of possibly solutions.
+
+One quick and easy way to verify that it is indeed a problem with your asset is to change to one of the system assets that is bundled with Xcode - these should launch with no problem
+
+### 3. Sometimes you might have to restart Xcode
+
+It's not uncommon for your app to get into a state where the black screen doesn't seem to go away, or your app never launches. Restarting Xcode usually fixes this.