Add build instructions for Linux packages.

Bug: 1042140
Change-Id: I6bf3b28d21c4f6918fe3dc7af52fb163fa22ec50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2001856
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Auto-Submit: Francois Marier <francois@brave.com>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732696}

chrome/installer/linux/BUILD.gn

@@ -174,6 +174,12 @@ action("strip_chrome_binary") {
 #
 # TO BUILD LINUX INSTALLER PACKAGES
 #
+# Use the following GN args:
+#
+#   is_component_build = false
+#
+# and the "chrome/installer/linux" target.
+#
 # The packages list the exact versions of each library used. The versions used
 # on the bots are likely different than those on your workstation, so you'll
 # get a stream of errors like: