Bitcode is part of App Thinning, which will be a feature of iOS 9. Basically when you submit to Apple you are uploading the intermediate representation of your code. Apple then optimizes that for the devices on download.
It is fine to disable it, you just won't get the benefits of that feature. To disable it just go to the your project’s Build Settings
in Xcode and search for Bitcode
, and set it to False.
To quote from the App Distribution Guide > App Thinning page by Apple.
Bitcode (iOS, watchOS)
Bitcode is an intermediate representation of a compiled program. Apps you upload to iTunes Connect that contain bitcode will be compiled and linked on the App Store. Including bitcode will allow Apple to re-optimize your app binary in the future without the need to submit a new version of your app to the store.
Note: For iOS apps, bitcode is the default, but optional. If you provide bitcode, all apps and frameworks in the app bundle need to include bitcode. For watchOS apps, bitcode is required.