gmtsar: remove orbits variant, add notes

- keep the configure argument
- add note on how to obtain/install the ORBITS data

science/gmtsar/Portfile

@@ -4,6 +4,7 @@ PortSystem          1.0
 
 name                gmtsar
 version             5.6
+revision            1
 categories          science
 platforms           darwin
 license             GPL-3
@@ -43,8 +44,15 @@ use_autoconf        yes
 
 use_parallel_build  no
 
-variant orbits description {Optional support for ERS-1/2 and Envisat satellites} {
-    depends_lib-append      port:gmtsar-data
-    configure.args-append   --with-orbits-dir=${prefix}/share/gmtsar-data/ORBITS
-}
+configure.args-append \
+                    --with-orbits-dir=${prefix}/share/gmtsar-data/ORBITS
 
+notes "
+If you require (optional) support for ERS-1/2 and Envisat satellites, please download the\
+ORITS data and copy it to ${prefix}/share/gmtsar-data.
+
+For example using:
+    mkdir -p gmtsar-data/ORBITS
+    curl -L ftp://topex.ucsd.edu/pub/gmtsar/ORBITS.tar | tar xv --directory gmtsar-data/ORBITS
+    sudo mv gmtsar-data ${prefix}/share/
+"