Split devtools documentation into per-tool files.

mojo/devtools/common/docs/mojo_run.md

+# mojo_run
+
+`mojo_run` allows you to run a Mojo shell either on the host, or on an attached
+Android device.
+
+```sh
+mojo_run APP_URL  # Run on the host.
+mojo_run APP_URL --android  # Run on Android device.
+mojo_run "APP_URL APP_ARGUMENTS"  # Run an app with startup arguments
+```
+
+Unless running within a Mojo checkout, we need to indicate the path to the shell
+binary:
+
+```sh
+mojo_run --shell-path path/to/shell/binary APP_URL
+```
+
+Some applications are meant to be run embedded in a **window manager**. To run
+these, you can pass the app url using the `--embed` flag. This will run the
+window manager and pass the given url to it:
+
+```sh
+mojo_run --embed APP_URL [--android]
+```
+
+By default, `mojo_run` uses https://core.mojoapps.io/kiosk_wm.mojo as the window
+manager. You can pass a different window manager url using the
+`--window-manager` flag to override this.