add comment about travis-wait

.travis.yml

@@ -12,6 +12,7 @@ matrix:
         - git checkout $TRAVIS_BRANCH
         - git reset --hard $TRAVIS_COMMIT
       script:
+        # Use travis-wait to allow slower tests to run
         - "cd test && travis_wait 30 python3 -m nose --rednose --verbose"
       env:
         PQCLEAN_ONLY_DIFF: 1
@@ -41,6 +42,7 @@ matrix:
         - ln -s /usr/local/bin/gcc-8 /usr/local/bin/gcc
         - gcc --version
       script:
+        # Use travis-wait to allow slower tests to run
         - "cd test && travis_wait 30 python3 -m nose --rednose --verbose"