Make it clear the requirements are Linux packages.

Add a space between the bullet point '-' and the package name.

R=johannkoenig@google.com

Change-Id: Iec44d755cc2540375dadfd6324dbe0c633c0db28
Reviewed-on: https://chromium-review.googlesource.com/1166160
Commit-Queue: Wan-Teh Chang <wtc@google.com>
Reviewed-by: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#581384}

third_party/libaom/cmake_update.sh

@@ -12,17 +12,18 @@
 # Usage:
 # $ ./cmake_update.sh
 # Requirements:
+# Install the following Debian packages.
 # - cmake3
 # - yasm or nasm
 # Toolchain for armv7:
-#  -gcc-arm-linux-gnueabihf
-#  -g++-arm-linux-gnueabihf
+# - gcc-arm-linux-gnueabihf
+# - g++-arm-linux-gnueabihf
 # Toolchain for arm64:
-#  -gcc-aarch64-linux-gnu
-#  -g++-aarch64-linux-gnu
+# - gcc-aarch64-linux-gnu
+# - g++-aarch64-linux-gnu
 # 32bit build environment for cmake. Including but potentially not limited to:
-#  -lib32gcc-7-dev
-#  -lib32stdc++-7-dev
+# - lib32gcc-7-dev
+# - lib32stdc++-7-dev
 # Alternatively: treat 32bit builds like Windows and manually tweak aom_config.h
 
 set -eE