Task #10975: INSTALL: add armadillo pkg name dependency for DPPP_DDECal

INSTALL

@@ -53,6 +53,7 @@ For Debian/Ubuntu (likely incomplete list, but goes a long way):
 	apt-get install libpng12-dev                         # or latest version; for AOFlagger
 	apt-get install libreadline-dev libpqxx-dev doxygen python-coverage  # optional
 	apt-get install libxml++2.6-dev                      # or newer
+        apt-get install libarmadillo-dev                     # optional, for DPPP_DDECal
 	apt-get install libunittest++-dev                    # optional, for tests that use UnitTest++
 	apt-get install python-xmlrunner                     # for some CEP/Pipeline/ tests
 	apt-get install python-pygresql python-psycopg2 python-mysql.connector  # python mysql and postgresql interfaces
@@ -66,6 +67,7 @@ For CentOS/Fedora (likely incomplete list, but goes a long way):
 	yum install boost-devel fftw-devel cfitsio-devel libxml2-devel libpng-devel
 	yum install readline-devel libpqxx-devel doxygen python-coverage  # optional
 	yum install libxml++-devel
+        yum install armadillo-devel                          # optional, for DPPP_DDECal
 	yum install PyGreSQL python-psycopg2 mysql-connector-python  # python mysql and postgresql interfaces
 	yum install python2-mock python-django               # for some SAS/ tests
 	yum install postgresql                               # optional, for some SAS/OTDB_Services/ tests