Fixed issue #943 and changed the docs accordingly

doc/help/commands.asciidoc

@@ -261,7 +261,7 @@ Start hinting.
  - With `spawn`: The executable and arguments to spawn.
  `{hint-url}` will get replaced by the selected
  URL.
- - With `userscript`: The userscript to execute.
+ - With `userscript`: The userscript to execute. Either store the userscript in your data directory or use an absolute path. 
  - With `fill`: The command to fill the statusbar with.
  `{hint-url}` will get replaced by the selected
  URL.
@@ -580,7 +580,7 @@ Note the {url} variable which gets replaced by the current URL might be useful h
 * +'cmdline'+: The commandline to execute.
 
 ==== optional arguments
-* +*-u*+, +*--userscript*+: Run the command as a userscript.
+* +*-u*+, +*--userscript*+: Run the command as a userscript. Either store it in your data directory or use an absolute path. 
 * +*-v*+, +*--verbose*+: Show notifications when the command started/exited.
 * +*-d*+, +*--detach*+: Whether the command should be detached from qutebrowser.
 

doc/userscripts.asciidoc

@@ -15,6 +15,10 @@ mpv, a simple key binding to something like `:spawn mpv {url}` should suffice.
 Also note userscripts need to have the executable bit set (`chmod +x`) for
 qutebrowser to run them.
 
+To call a userscript, it needs to be stored in your data directory under
+`userscripts` (for example: `~/.local/share/qutebrowser/userscripts/myscript`), 
+or just use an absolute path.
+
 Getting information
 -------------------
 

qutebrowser/commands/userscripts.py

@@ -344,6 +344,14 @@ def run(cmd, *args, win_id, env, verbose=False):
     if user_agent is not None:
         env['QUTE_USER_AGENT'] = user_agent
     cmd = os.path.expanduser(cmd)
+
+    # check if userscript is in absolute path or in $XDG_DATA_DIRS
+    if not os.path.isabs(cmd) :
+        log.misc.debug("{} is no absoulte path".format(cmd))
+        c = os.path.join(standarddir.data(),"userscripts", cmd)
+        if os.path.isfile(c):
+            cmd = c
+
     runner.run(cmd, *args, env=env, verbose=verbose)
     runner.finished.connect(commandrunner.deleteLater)
     runner.finished.connect(runner.deleteLater)