WIP: Migrate Wiki content over to src/docs

docs/linux_password_storage.md

+# Introduction
+
+On Linux, Chromium can store passwords in three ways:
+  * GNOME Keyring
+  * KWallet 4
+  * plain text
+Chromium chooses which store to use automatically, based on your desktop environment.
+
+Passwords stored in GNOME Keyring or KWallet are encrypted on disk, and access to them is controlled by dedicated daemon software. Passwords stored in plain text are not encrypted. Because of this, when either GNOME Keyring or KWallet is in use, any unencrypted passwords that have been stored previously are automatically moved into the encrypted store.
+
+Support for using GNOME Keyring and KWallet was added in version 6, but using these (when available) was not made the default mode until version 12.
+
+# Details
+
+Although Chromium chooses which store to use automatically, the store to use can also be specified with a command line argument:
+  * `--password-store=gnome` (to use GNOME Keyring)
+  * `--password-store=kwallet` (to use KWallet)
+  * `--password-store=basic` (to use the plain text store)
+
+Note that Chromium will fall back to `basic` if a requested or autodetected store is not available.
+
+In versions 6-11, the store to use was not detected automatically, but detection could be requested with an additional argument:
+  * `--password-store=detect`