Add Cargo package for inline table of contents

.gitlab-ci.yml

@@ -9,10 +9,11 @@ pages:
   before_script:
     - export PATH="$PATH:$CARGO_HOME/bin"
     - mdbook --version || cargo install --debug mdbook
+    - cargo install mdbook-toc
   script:
         - mdbook build -d public
   only:
-      - master 
+      - master
   artifacts:
       paths:
           - public