Improve install.sh's opening header:

Direct end users to use package management if feasible.
Direct advanced developers to use CMake.
Redraw dependency tree lines without special characters.
Instruct users to use --yes-to-all for interactive builds.
Recommend --help to see installation options.

Author: Damian Rouson

prerequisites/install-functions/print_header.sh

@@ -10,30 +10,39 @@ print_header() {
   m4ver="$("${__file}" -V m4)"
   popd >/dev/null
   clear
-  echo ""
-  echo "*** By default, building OpenCoarrays requires CMake ${cmakever} or later,      ***"
-  echo "*** MPICH ${mpichver}, and GCC Fortran (gfortran) ${gccver} or later.  To see         ***"
-  echo "*** options for forcing the use of older or alternative packages, execute ***"
-  echo "*** this script with the -h flag.  This script will recursively traverse  ***"
-  echo "*** the following dependency tree, asking permission to download, build,  ***"
-  echo "*** and install any packages that are required for building another       ***"
-  echo "*** package and are neither in your PATH nor in                           ***"
-  echo "*** opencoarrays/prerequisites/installations:                             ***"
+  echo "__________ Please read these instructions carefully before proceeding. ___________"
+  echo "__________________________________________________________________________________"
+  echo "*** Most end users will find it easier to install OpenCoarrays via the native  ***"
+  echo "*** package manager for the target operating system.  Advanced developers will ***"
+  echo "*** find it best to install via CMake.  Please see the OpenCoarrays README.md  ***"
+  echo "*** for a list of supported package installers or for instructions on using    ***"
+  echo "*** CMake to install.  The current script offers a fallback when other methods ***"
+  echo "*** prove infeasible. This script builds any missing prerequisites from source ***"
+  echo "*** and then builds OpenCoarrays from source.  The process might take a few    ***"
+  echo "*** minutes if the script finds all prerequisites or several hours if the      ***"
+  echo "*** script finds no prerequisites. (Run './install.sh --help' without quotes   ***"
+  echo "*** to see the installation options.)  This script traverses the following     ***"
+  echo "*** dependency tree and asks permission to install packages that are not in    ***"
+  echo "*** your PATH, not in the prerequisites/installations subdirectory of the      ***"
+  echo "*** OpenCoarrays source tree, or have insufficiently recent version numbers:   ***"
   echo ""
   # Generate the following text using the `tree` command w/ dummy directory structure
   cat <<-EOF
     opencoarrays
-    ├── cmake-${cmakever}
-    └── mpich-${mpichver}
-        └── gcc-${gccver}
-            ├── flex-${flexver}
-            │   └── bison-${bisonver}
-            │       └── m4-${m4ver}
-            ├── gmp
-            ├── mpc
-            └── mpfr
+    |__ cmake-${cmakever}
+    |__ mpich-${mpichver}
+        |__ gcc-${gccver}
+            |__ flex-${flexver}
+            |   |__ bison-${bisonver}
+            |       |__ m4-${m4ver}
+            |__ gmp
+            |__ mpc
+            |__ mpfr
 
 EOF
+  echo "*** For a non-interactive installation, relaunch this script with the command  ***"
+  echo "*** './install.sh --yes-to-all' without quotes to instruct the script to       ***"
+  echo "*** assume affirmative answers to all user queries.                            ***"
   echo ""
   printf "%s will be installed in %s\n" "${arg_p}" "${install_path}"
   echo ""