Generalize comment on excluding .git

Signed-off-by: Anna Rift <anna.rift@hpe.com>

Dockerfile

@@ -71,7 +71,7 @@ RUN make cleanall
 # Hack to get access to Chapel binaries
 RUN cd $CHPL_HOME/bin && ln -s */* .
 
-# The .git folder is huge and we really don't need it.
+# Remove some unneeded files to reduce image size
 RUN rm -rf .git
 RUN for subdir in `ls test || true`; do \
       if [ "$subdir" != "release" ]; then \