Update Troubleshooting with different iOS fix.

Troubleshooting.md

@@ -13,3 +13,26 @@ well, but you can have 33.0.2 installed in addition to other versions.
 
 To install new build tools, go to Tools -> Android -> SDK Manager, SDK Tools tab, check "Show Package Details" at the
 bottom, select Build Tools version 33.0.2, and click Apply or OK. Then follow the installation steps.
+
+### When importing an iOS project, an error mentions SeekableByteChannel.
+
+Like the above error, this involves `void org.apache.commons.compress.archivers.zip.ZipFile.<init>(java.nio.channels.SeekableByteChannel)'`.
+This has to do with the placement of the `robovm` plugin, which as of RoboVM 2.3.19 needs to be in `ios/build.gradle`,
+not the root `build.gradle`. This will be automatically fixed in projects generated by gdx-liftoff 1.12.0.1, but until
+then, you can replace the top of `ios/build.gradle` with:
+```gradle
+buildscript {
+  repositories {
+    mavenCentral()
+  }
+  dependencies {
+    classpath "com.mobidevelop.robovm:robovm-gradle-plugin:$robovmVersion"
+  }
+}
+apply plugin: 'robovm'
+
+[compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
+```
+(Starting with the line that sets encoding, everything else is the same.) You will also need to remove any mention of
+`robovm` plugin from the top of the root `build.gradle` file; this means a line that starts with `classpath` and a line
+`apply plugin: 'robovm'`.