Task #9537: update INSTALL

INSTALL

@@ -33,7 +33,7 @@ Install from Ubuntu Packages (or a Docker image / script)
 ---------------------------------------------------------
 
 To install LOFAR Offline processing tools (and many more radio astro packages)
-the easy way for Ubuntu LTS version(s), see:
+the easy way for Ubuntu LTS 16.04, see:
 
 	KERN: The Radio Astronomy Software Suite
 	http://kernsuite.info/
@@ -100,7 +100,7 @@ Instructions for Manual Build from Source
   into e.g. $HOME/local/$LOFAR_RELEASE/
   (Only ends succesfully once CMake can find all required dependencies.)
 
-	mkdir -p $HOME/build/$LOFAR_RELEASE/gnu_opt  # last directory must be {gnu|clang}_{debug|opt}
+	mkdir -p $HOME/build/$LOFAR_RELEASE/gnu_opt  # last directory must be {gnu|clang}[cxx11]_{debug|opt}
 	cd $HOME/build/$LOFAR_RELEASE/gnu_opt
 	cmake -DCMAKE_INSTALL_PREFIX="$HOME/local/$LOFAR_RELEASE" -DBUILD_PACKAGES="DP3 Calibration Imager PyBDSM" -DUSE_OPENMP=ON "$HOME/src/$LOFAR_RELEASE"