Add docs for recently introduced new middle command line options

Author: joto

docs/osm2pgsql.md

@@ -171,6 +171,19 @@ mandatory for short options too.
 :   Set ID shift for way node bucket index in middle. Experts only. See
     documentation for details.
 
+\--middle-database-format=FORMAT
+:   Set the database format for the middle tables to FORMAT. Allowed formats
+    are **legacy** and **new**. The **legacy** format is the old format that
+    will eventually be deprecated and removed but is currently still the
+    default. The **new** format was introduced in version 1.9.0 and is still
+    experimental. See the manual for details on these formats. (Only works
+    with **\--slim**. In append mode osm2pgsql will automatically detect the
+    database format, so don't use this with **-a, \--append**.)
+
+\--middle-with-nodes
+:   Used together with the **new** middle database format when a flat nodes
+    file is used to force storing nodes with tags in the database, too.
+
 # OUTPUT OPTIONS
 
 -O, \--output=OUTPUT

src/command-line-parser.cpp

@@ -183,6 +183,8 @@ Middle options:\n\
                     id, timestamp and version) for each object in the database.\n\
        --middle-schema=SCHEMA  Schema to use for middle tables (default: none).\n\
        --middle-way-node-index-id-shift=SHIFT  Set ID shift for bucket index.\n\
+       --middle-database-format=FORMAT  Set middle db format (default: legacy).\n\
+       --middle-with-nodes  Store tagged nodes in db (new middle db format only).\n\
 \n\
 Pgsql output options:\n\
     -i|--tablespace-index=TBLSPC  The name of the PostgreSQL tablespace where\n\