Add --slurpfile

docs/content/3.manual/manual.yml

@@ -209,13 +209,18 @@ sections:
         predefined variable. If you run jq with `--argjson foo 123`, then
         `$foo` is available in the program and has the value `123`.
 
-      * `--argfile name filename`:
+      * `--slurpfile variable-name filename`:
 
-        This option passes the first value from the named file as a
-        value to the jq program as a predefined variable. If you run jq
-        with `--argfile foo bar`, then `$foo` is available in the
-        program and has the value resulting from parsing the content of
-        the file named `bar`.
+        This option reads all the JSON texts in the named file and binds
+        an array of the parsed JSON values to the given global variable.
+        If you run jq with `--argfile foo bar`, then `$foo` is available
+        in the program and has an array whose elements correspond to the
+        texts in the file named `bar`.
+
+      * `--argfile variable-name filename`:
+
+        Like `--slurpfile`, but uses just the first value in the given
+        file.
 
   - title: Basic filters
     entries: