phobos.el: add commentary

phobos.el

@@ -21,6 +21,18 @@
 ;; You should have received a copy of the GNU General Public License
 ;; along with phobos.el.  If not, see <https://www.gnu.org/licenses/>.
 
+;;; Commentary:
+
+;; phobos.el provides several functions for viewing Phobos documentation
+;; and documentation for other D libraries. These functions open the
+;; documentation in a web browser, calling the process `phobos-browser'.
+
+;; These functions are provided:
+;;  * `phobos': view Phobos documentation
+;;  * `dub-doc': view documentation for a symbol in a dub package
+;;  * `describe-dub-package': view the home page for a dub package
+;; An alias `view-dub-documentation' also exists for `dub-doc'.
+
 ;;; Code:
 
 (defgroup phobos nil