Update usage.rst

Author: fxwiegand

src/docs/usage.rst

@@ -4,6 +4,12 @@
 Usage
 *****
 
+.. code-block:: bash
+
+    alignoth
+
+To activate the interactive mode guiding you through the process of creating an alignment plot.
+
 .. code-block:: bash
 
     alignoth -b path/to/my.bam -r path/to/my/reference.fa -g chr1:200-300 > plot.vl.json