Add Android fonts to blimp engine

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
@@ skipping 82 matching lines @@
 ./build/android/adb_reverse_forwarder.py --debug -v 25467 25467
 ```
 
 ### Required engine binary flags
 * `--blimp-client-token-path=$PATH`: Path to a file containing a nonempty
   token string. If this is not present, the engine will fail to boot.
 * `--use-remote-compositing`: Ensures that the renderer uses the remote
   compositor.
 * `--disable-cached-picture-raster`: Ensures that rasterized content is not
   destroyed before serialization.
+* `--android-fonts-path=$PATH`: Path to where the fonts are located.
+  Typically this would be `out-linux/Debug/gen/third_party/blimp_fonts`.
 
 #### Typical invocation
 When the client connects to a manually specified engine instead of using the
 assigner, it will use a dummy token. The engine needs to know what this token
 is, so it must be provided using the `--blimp-client-token-path` flag. The token
 is available in the constant `kDummyClientToken` in
 `blimp/client/session/assignment_source.h`. You can easily store that to a file
 by running the following command once:
 
 ```bash
 awk '{if ( match($0, /^\s*const char kDummyClientToken.*/) ) { print substr($5, 2, length($5)-3);} }' \
   ./blimp/client/session/assignment_source.h > /tmp/blimpengine-token
 ```
 
 Then start the engine using these flags:
 
 ```bash
 out-linux/Debug/blimp_engine_app \
   --use-remote-compositing \
   --disable-cached-picture-raster \
   --blimp-client-token-path=/tmp/blimpengine-token \
   --user-data-dir=/tmp/blimpengine \
+  --android-fonts-path=out-linux/Debug/gen/third_party/blimp_fonts \
   --enable-logging=stderr \
   --vmodule="blimp*=1"
 ```