Add assigner support to Blimp

blimp/docs/running.md

 # Running Blimp
 
 See [build](build.md) for instructions on how to build Blimp.
 
 ## Running the client
 
 There are both Android and Linux clients.  The Android client is the shipping
 client while the Linux client is used for development purposes.
 
 ### Android Client
 
 Install the Blimp APK with the following:
 
 ```bash
 ./build/android/adb_install_apk.py $(PRODUCT_DIR)/apks/Blimp.apk
 ```
 
 Set up any command line flags with:
 
 ```bash
 ./build/android/adb_blimp_command_line --enable-webgl
 ```
 
+To have the client connect to a custom engine use the `--blimplet-endpoint`
+flag.  This takes values in the form of scheme:ip:port.  The possible valid
+schemes are 'tcp', 'quic', and 'ssl'.  An example valid endpoint would be
+`--blimplet-endpoint=tcp:127.0.0.1:500`.
+
 Run the Blimp APK with:
 
 ```bash
 adb_run_blimp_client
 ```
 
 ### Linux Client
 
 TBD
 
 ## Running the engine
 
 ### In a container
 For running the engine in a container, see [container](container.md).
 
 ### On a workstation
 If you are running the engine on your workstation and are connected to the
 client device via USB, you'll need remote port forwarding to allow the Blimp
 client to talk to your computer. Follow the instructions
 [here](https://developer.chrome.com/devtools/docs/remote-debugging) to get
 started. You'll probably want to remap 25467 to "localhost:25467".
 
 ### Required flags
 *   `--blimp-client-token-path=$PATH`: Path to a file containing a nonempty
 token string. If this is not present, the engine will fail to boot.
+