tweak scripts & docs for iOS build on new device

BUILDING.md

@@ -1126,7 +1126,7 @@ If you need to build manually or want to understand the individual steps:
 
 ##### 0. First time (or if dependencies change)
 
-- `pkgx +rubygems.org zsh`
+- `pkgx +rubygems.org +pod zsh`
 
 - ... and you may have to fix these, especially with pkgx:
 
@@ -1153,6 +1153,8 @@ Here's prod. Also available: test, dev
 npm run build:ios:prod
 ```
 
+- The first time, it may complain about a bundler install for "missing gems", and you'll want to run the "install" command it gives you.
+
 3.1. Use Xcode to build and run on simulator or device.
 
 - Select Product -> Destination with some Simulator version. Then click the run arrow.