Add FreeBSD port info to INSTALL.md

Author: Damian Rouson

INSTALL.md

@@ -17,6 +17,7 @@ Download this file as a PDF document
   * [macOS]
   * [Windows]
   * [Linux]
+  * [FreeBSD]
   * [Virtual machine]
   * [Installation Script]
 * [Advanced Installation from Source]
@@ -127,6 +128,14 @@ feature request via our [Issues] page.
 
 [top]
 
+### FreeBSD ###
+
+A FreeBSD Port is available for installing OpenCoarrays and can be
+located via [port search].  See the FreeBSD OpenCoarrays [port details] 
+page for installation instructions.
+
+[top]
+
 ## Virtual machine ##
 
 Users of macOS, Windows, or Linux have the option to use OpenCoarrays
@@ -402,3 +411,5 @@ export gcc_install_path=/desired/installation/destination
 [commit comment 20539810]: https://github.com/sourceryinstitute/OpenCoarrays/commit/26e99919fe732576f7277a0e1b83f43cc7c9d749#commitcomment-20539810
 [Homebrew]: https://brew.sh
 [dnf]: https://github.com/rpm-software-management/dnf
+[port details]: http://www.freshports.org/lang/opencoarrays
+[port search]: https://www.freebsd.org/cgi/ports.cgi?query=opencoarrays