Add hint for OR'ing TERMs to help text for ls/list.

The regexp syntax and quoting rules aren't known to many who are not well versed in the Bash shell, and difficult to get right even for people in the know. This question came up just recently on the mailing list, too.

todo.sh

@@ -87,10 +87,10 @@ help()
 
 		  Options:
 		    -@
-		        Hide context names in list output. Use twice to show context
+		        Hide context names in list output.  Use twice to show context
 		        names (default).
 		    -+
-		        Hide project names in list output. Use twice to show project
+		        Hide project names in list output.  Use twice to show project
 		        names (default).
 		    -c
 		        Color mode
@@ -103,7 +103,7 @@ help()
 		    -p
 		        Plain mode turns off colors
 		    -P
-		        Hide priority labels in list output. Use twice to show
+		        Hide priority labels in list output.  Use twice to show
 		        priority labels (default).
 		    -a
 		        Don't auto-archive tasks automatically on completion
@@ -199,12 +199,15 @@ help()
 		    list [TERM...]
 		    ls [TERM...]
 		      Displays all tasks that contain TERM(s) sorted by priority with line
-		      numbers.  If no TERM specified, lists entire todo.txt.
+		      numbers.  Each task must match all TERMs (logical AND); to display
+		      tasks that contain any TERM (logical OR), use
+		      "TERM1\|TERM2\|..." (with quotes), or TERM1\\\|TERM2 (unquoted).
+		      If no TERM specified, lists entire todo.txt.
 
 		    listall [TERM...]
 		    lsa [TERM...]
 		      Displays all the lines in todo.txt AND done.txt that contain TERM(s)
-		      sorted by priority with line  numbers.  If no TERM specified, lists
+		      sorted by priority with line numbers.  If no TERM specified, lists
 		      entire todo.txt AND done.txt concatenated and sorted.
 
 		    listcon
@@ -214,8 +217,8 @@ help()
 		    listfile [SRC [TERM...]]
 		    lf [SRC [TERM...]]
 		      Displays all the lines in SRC file located in the todo.txt directory,
-		      sorted by priority with line  numbers.  If TERM specified, lists
-		      all lines that contain TERM in SRC file.
+		      sorted by priority with line numbers.  If TERM specified, lists
+		      all lines that contain TERM(s) in SRC file.
 		      Without any arguments, the names of all text files in the todo.txt
 		      directory are listed.
 
@@ -223,7 +226,7 @@ help()
 		    lsp [PRIORITY] [TERM...]
 		      Displays all tasks prioritized PRIORITY.
 		      If no PRIORITY specified, lists all prioritized tasks.
-		      If TERM specified, lists only prioritized tasks that contain TERM.
+		      If TERM specified, lists only prioritized tasks that contain TERM(s).
 
 		    listproj
 		    lsprj