Minor updates to the help message printed by build_ios_libs.sh (with -h)

webrtc/build/ios/build_ios_libs.sh

Index: webrtc/build/ios/build_ios_libs.sh
diff --git a/webrtc/build/ios/build_ios_libs.sh b/webrtc/build/ios/build_ios_libs.sh
index 4c78da58fcdfd3c98489cc43aa80a9e0136bf35d..a772b558d97059e303172acef9de51dfd125c57c 100755
--- a/webrtc/build/ios/build_ios_libs.sh
+++ b/webrtc/build/ios/build_ios_libs.sh
@@ -90,14 +90,14 @@ use_xcode_clang=true is_component_build=false"
 function usage {
   echo "WebRTC iOS FAT libraries build script."
   echo "Each architecture is compiled separately before being merged together."
-  echo "By default, the fat libraries will be created in out_ios_libs/."
+  echo "By default, the library is created in out_ios_libs/. (Change with -o.)"
   echo "The headers will be copied to out_ios_libs/include."
-  echo "Usage: $0 [-h] [-b build_type] [-c] [-o output_dir]"
+  echo "Usage: $0 [-h] [-b build_type] [-c] [-o output_dir] [-r rev_num] [-e]"
   echo "  -h Print this help."
-  echo "  -b The build type. Can be framework or static_only."
-  echo "     Defaults to framework."
-  echo "  -c Removes generated build output."
-  echo "  -o Specifies a directory to output build artifacts to."
+  echo "  -b The build type. Can be \"framework\" or \"static_only\"."
+  echo "     Defaults to \"framework\"."
+  echo "  -c Removes the previously generated build output, if any."
+  echo "  -o Specifies a directory to output the build artifacts to."
   echo "     If specified together with -c, deletes the dir."
   echo "  -r Specifies a revision number to embed if building the framework."
   echo "  -e Compile with bitcode."