docs/linux_proxy_config.md

+# Linux Proxy Config
+
+Chromium on Linux has several possible sources of proxy info: GNOME/KDE
+settings, command-line flags, and environment variables.
+
+## GNOME and KDE
+
+When Chromium detects that it is running in GNOME or KDE, it will automatically
+use the appropriate standard proxy settings. You can configure these proxy
+settings from the options dialog (the "Change proxy settings" button in the
+"Under the Hood" tab), which will launch the GNOME or KDE proxy settings
+applications, or by launching those applications directly.
+
+## Flags and environment variables
+
+For other desktop environments, Chromium's proxy settings can be configured
+using command-line flags or environment variables. These are documented on the
+man page (`man google-chrome` or `man chromium-browser`).