Document genbki.sh's ability to auto-assign OIDs for DESCR macros.

Some other minor wording improvements.

src/backend/catalog/README

-$Header: /cvsroot/pgsql/src/backend/catalog/README,v 1.4 2002/03/22 20:14:42 tgl Exp $
+$Header: /cvsroot/pgsql/src/backend/catalog/README,v 1.5 2002/04/08 22:09:05 tgl Exp $
 
 This directory contains .c files that manipulate the system catalogs
 as well as .h files that define the structure of the system catalogs.
@@ -27,9 +27,9 @@ of cross-references from other pre-loaded tuples.  For example, pg_type
 contains pointers into pg_proc (e.g., pg_type.typinput), and pg_proc
 contains back-pointers into pg_type (pg_proc.proargtypes).  For such
 cases, the OID assigned to a tuple may be explicitly set by use of the
-"OID =" clause of the .bki insert statement.  If no such pointers are
-required to a given tuple, then the OID may be set to the wildcard value 0
-(i.e., the system generates a random OID in the usual way, or leaves it
+"OID = n" clause of the .bki insert statement.  If no such pointers are
+required to a given tuple, then the OID = n clause may be omitted
+(then the system generates a random OID in the usual way, or leaves it
 0 in a catalog that has no OIDs).  In practice we usually preassign OIDs
 for all or none of the pre-loaded tuples in a given catalog, even if only
 some of them are actually cross-referenced.
@@ -39,16 +39,28 @@ be known directly in the C code.  In such cases, put a #define in the
 catalog's .h file, and use the #define symbol in the C code.  Writing
 the actual numeric value of any OID in C code is considered very bad form.
 (Direct references to pg_proc OIDs are common enough that there's a special
-mechanism to create the necessary #define's automatically.  For all the
-other system catalogs, you have to manually create any #define's you need.)
+mechanism to create the necessary #define's automatically: see
+backend/utils/Gen_fmgrtab.sh.  For all the other system catalogs, you have
+to manually create any #define's you need.)
 
 - If you need to find a valid OID for a tuple that will be referred to by
 others, use the unused_oids script.  It generates inclusive ranges of
-*unused* OIDs (i.e., the line "45-900" means OIDs 45 through 900 have
+*unused* OIDs (e.g., the line "45-900" means OIDs 45 through 900 have
 not been allocated yet).  Currently, OIDs 1-9999 are reserved for manual
 assignment; the unused_oids script simply looks through the include/catalog
 headers to see which ones do not appear in "OID =" clauses.
 
+- OIDs 10000-16383 are reserved for assignment by the genbki.sh script:
+it will insert these OIDs if it sees a clause "OID = 0" in a DATA
+statement.  You would typically use this feature if you don't care exactly
+which OID is assigned to a catalog row (because it has no cross-references
+you need to hardwire) but you want to give it a DESCR entry.  The DESCR macro
+will not work for rows that don't have any OID at genbki.sh time.
+
+- The OID counter starts at 16384 at bootstrap.  If a catalog row is in a
+table that requires OIDs, but no OID was preassigned by hand or by genbki.sh,
+then it will receive an OID of 16384 or above.
+
 - To create a "BOOTSTRAP" table you have to do a lot of extra work: these
 tables are not created through a normal CREATE TABLE operation, but spring
 into existence when first written to during initdb.  Therefore, you must
@@ -58,7 +70,7 @@ heap_create() in heap.c to force the correct OID to be assigned when the table
 is first referenced.  (It's near the top of the function with the comment
 beginning in 'Real ugly stuff'.)  Avoid making new catalogs be bootstrap
 catalogs if at all possible; generally, only tables that must be written to
-to create a table should be bootstrapped.
+in order to create a table should be bootstrapped.
 
 - Certain BOOTSTRAP tables must be at the start of the Makefile
 POSTGRES_BKI_SRCS variable, as these will not be created through standard