Document travis keys used in .travis.yml

.travis.yml

@@ -132,6 +132,8 @@ jobs:
     - *gcc_environment
     before_deploy:
       - .travis/bintray_json.sh
+    # deploy to bintray if we're in the souffle-lang repo
+    # https://docs.travis-ci.com/user/deployment/bintray
     deploy:
       - provider: bintray
         skip-cleanup: true
@@ -163,6 +165,8 @@ jobs:
         - doxygen
         - graphviz
     script: "./bootstrap && ./configure && make doxygen-doc"
+    # update the gh-pages branch with doxygen output if the required github token has been set
+    # https://pages.github.com/
     deploy:
       provider: pages
       skip-cleanup: true