update readme

README.md

@@ -232,15 +232,18 @@ import Amplitude_iOS
 In either case, you can call Amplitude methods with `Amplitude.instance().method(...)`
 
 # Advanced #
+This SDK automatically grabs useful data from the phone, including app version, phone model, operating system version, and carrier information.
 
-This SDK automatically grabs useful data from the phone, including app version, phone model, operating system version, and carrier information. If the user has granted your app location permissions, the SDK will also grab the location of the user. Amplitude will never prompt the user for location permissions itself, this must be done by your app. Amplitude only polls for a location once on startup of the app, once on each app open, and once when the permission is first granted. There is no continuous tracking of location, although you can force Amplitude to grab the latest location by calling `[[Amplitude instance] updateLocation]`. Note this does consume more resources on the user's device, so use this wisely. If you wish to disable location tracking done by the app, you can call `[[Amplitude instance] disableLocationListening]` at any point. If you want location tracking disabled on startup of the app, call disableLocationListening before you call `initializeApiKey:`. You can always reenable location tracking through Amplitude with `[[Amplitude instance] enableLocationListening]`.
-
-User IDs are automatically generated and will default to device specific identifiers if not specified.
+### Location Tracking ###
+If the user has granted your app location permissions, the SDK will also grab the location of the user. Amplitude will never prompt the user for location permissions itself, this must be done by your app. Amplitude only polls for a location once on startup of the app, once on each app open, and once when the permission is first granted. There is no continuous tracking of location, although you can force Amplitude to grab the latest location by calling `[[Amplitude instance] updateLocation]`. Note this does consume more resources on the user's device, so use this wisely. If you wish to disable location tracking done by the app, you can call `[[Amplitude instance] disableLocationListening]` at any point. If you want location tracking disabled on startup of the app, call disableLocationListening before you call `initializeApiKey:`. You can always reenable location tracking through Amplitude with `[[Amplitude instance] enableLocationListening]`.
 
+### Custom Device IDs ###
 Device IDs are randomly generated. You can, however, choose to instead use the identifierForVendor (if available) by calling `[[Amplitude instance] useAdvertisingIdForDeviceId]` before initializing with your API key. You can also retrieve the Device ID that Amplitude uses with `[[Amplitude instance] getDeviceId]`.
 
 If you have your own system for tracking device IDs and would like to set a custom device ID, you can do so with `[[Amplitude instance] setDeviceId:@"CUSTOM_DEVICE_ID"];` **Note: this is not recommended unless you really know what you are doing.** Make sure the device ID you set is sufficiently unique (we recommend something like a UUID - see `[AMPUtils generateUUID]` for an example on how to generate) to prevent conflicts with other devices in our system.
 
+### ARC ###
 This code will work with both ARC and non-ARC projects. Preprocessor macros are used to determine which version of the compiler is being used.
 
+### SSL pinning ###
 The SDK includes support for SSL pinning, but it is undocumented and recommended against unless you have a specific need. Please contact Amplitude support before you ship any products with SSL pinning enabled so that we are aware and can provide documentation and implementation help.