Add documentation on inclusion of own repositories

docs/usage.rst

@@ -36,6 +36,17 @@ SGE. To use the cluster set the `-C` option.
 
   psot analyze -f myfasta.faa -o results -p fast -l -C
 
+Include own repository
+----------------------
+
+To include your own repositories, set the PSOT_REPOSITORIES environment variable.
+
+::
+
+  export PSOT_REPOSITORIES=<path1>:<path2>
+  psot analyze -f myfasta.faa -o results -p my_profile 
+
+
 Debug mode execution
 --------------------