Spelling fix, comments explaining script.

R=mtklein@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/261913006

git-svn-id: http://skia.googlecode.com/svn/trunk@14565 2bbb7eff-a529-9590-31e7-b0007b416f81

tools/install_dependencies.sh

@@ -4,6 +4,10 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# install_dependencies.sh will install system-specific Skia
+# dependencies using your system's package manager.  If your system is
+# not supported, add logic here to support it.
+
 if command -v lsb_release > /dev/null ; then
     case $(lsb_release -i -s) in
         Ubuntu)