Clarify what is done in the Travis configuration

.travis.yml

@@ -29,6 +29,7 @@ notifications:
 language: java
 install:
   - |
+    # Fail if any of the following commands fails.
     set -e
     # Parallelize downloads of dependencies.
     sudo pip install Sphinx==1.1.3 &
@@ -50,10 +51,15 @@ install:
     wait ${GRADLE_PID}
 script:
   - |
+    # Fail if any of the following commands fails.
     set -e
+    
+    # Ant-based tests: run unit-tests, build the web UI, build HTML+PDF docs.
     ant test
     ant gwtc
     ant docs
+    
+    # Bazel-based tests: unit tests and building the JAR file.
     bazel test //src/test/java/org/edumips64/...:all
     bazel build //src/main/java/org/edumips64:edumips64_deploy.jar --workspace_status_command=utils/bazel-stamp.sh --stamp
 jdk: