Update docs for building Chromium on Crostini

install-build-deps requires lsb_release, add a note for Crostini
to install lsb-release before running install-build-deps

Bug: None
Test: sudo apt install lsb-release; install-build-deps.sh --no-arm
Change-Id: I642275a4aa6ac22ff9c71733a4b4911db23bc392
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1716605
Auto-Submit: David Munro <davidmunro@google.com>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680354}

docs/linux_build_instructions.md

@@ -356,10 +356,10 @@ For the optional packages on Arch Linux:
 
 ### Crostini (Debian based)
 
-First install the `file` command for the script to run properly:
+First install the `file` and `lsb-release` commands for the script to run properly:
 
 ```shell
-$ sudo apt-get install file
+$ sudo apt-get install file lsb-release
 ```
 
 Then invoke install-build-deps.sh with the `--no-arm` argument,