install dependencies in rustdoc workflow

.github/workflows/rustdoc.yml

@@ -8,6 +8,8 @@ jobs:
     name: Deploy Documentation
     runs-on: ubuntu-latest
     steps:
+    - name: Install dependencies
+      run: sudo apt -y install libglib2.0-dev libgstreamer1.0-dev libnice-dev
     - name: Check out
       uses: actions/checkout@v1
     - name: Install Rust toolchain