bdev_module.h: replace outdated docs with link

The bdev module writer's guide at the top of bdev_module.h is outdated;
replace it with a link to the up-to-date documentation in
doc/bdev_module.md.

Change-Id: I36f745f70596b9e4c9a7495a019a03268460d2dd
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/412539
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>

include/spdk/bdev_module.h

@@ -34,6 +34,8 @@
 
 /** \file
  * Block Device Module Interface
+ *
+ * For information on how to write a bdev module, see @ref bdev_module.
  */
 
 #ifndef SPDK_BDEV_MODULE_H
@@ -47,35 +49,6 @@
 #include "spdk/io_channel.h"
 #include "spdk/uuid.h"
 
-/** \page block_backend_modules Block Device Backend Modules
- *
- * To implement a backend block device driver, a number of functions
- * dictated by struct spdk_bdev_fn_table must be provided.
- *
- * The module should register itself using SPDK_BDEV_MODULE_REGISTER to
- * define the parameters for the module.
- *
- * <hr>
- *
- * In the module initialization code, the config file sections can be parsed to
- * acquire custom configuration parameters. For example, if the config file has
- * a section such as below:
- * <blockquote><pre>
- * [MyBE]
- * MyParam 1234
- * </pre></blockquote>
- *
- * The value can be extracted as the example below:
- * <blockquote><pre>
- * struct spdk_conf_section *sp = spdk_conf_find_section(NULL, "MyBe");
- * int my_param = spdk_conf_section_get_intval(sp, "MyParam");
- * </pre></blockquote>
- *
- * The backend initialization routine also need to create "disks". A virtual
- * representation of each LUN must be constructed. Mainly a struct spdk_bdev
- * must be passed to the bdev database via spdk_bdev_register().
- */
-
 /** Block device module */
 struct spdk_bdev_module {
 	/**