Add documentation in password_fill

Describe usage and configuration. Also allow "login:" as a prefix for
login name in pass entries.

misc/userscripts/password_fill

@@ -15,6 +15,13 @@ directly ask me via IRC (nickname thorsten\`) in #qutebrowser on freenode.
 Usage: run as a userscript form qutebrowser, e.g.:
   spawn --userscript ~/.config/qutebrowser/password_fill
 
+Pass backend: (see also passwordstore.org)
+  This script expects pass to store the credentials of each page in an extra
+  file, where the filename (or filepath) contains the domain of the respective
+  page. The first line of the file must contain the password, the login name
+  must be contained in a later line beginning with "user:", "login:", or
+  "username:" (configurable by the user_pattern variable).
+
 Behaviour:
   It will try to find a username/password entry in the configured backend
   (currently only pass) for the current website and will load that pair of
@@ -24,11 +31,16 @@ Behaviour:
   If no entry is found, then it crops subdomains from the url if at least one
   entry is found in the backend. (In that case, it always shows a menu)
 
+Configuration:
+  This script loads the bash script ~/.config/qutebrowser/password_fill_rc (if
+  it exists), so you can change any configuration variable and overwrite any
+  function you like.
+
 EOF
 }
 
 set -o pipefail
-shopt -s nocasematch
+shopt -s nocasematch # make regexp matching in bash case insensitive
 
 if [ -z "$QUTE_FIFO" ] ; then
     help
@@ -196,7 +208,7 @@ match_filename=1 # whether allowing entry match by filepath
 match_line=0     # whether allowing entry match by URL-Pattern in file
                  # Note: match_line=1 gets very slow, even for small password stores!
 match_line_pattern='^url: .*' # applied using grep -iE
-user_pattern='^(user|username): '
+user_pattern='^(user|username|login): '
 
 GPG_OPTS=( "--quiet" "--yes" "--compress-algo=none" "--no-encrypt-to" )
 GPG="gpg"