blockdev: add page

[DarkMatter-999]

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page(s) have at most 8 examples.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The page(s) follow the style guide.
• The PR title conforms to the recommended templates.

Solves #13699

[sebastiaanspeck]

Thank you for your first. Please make sure to read the style guide and contributing guide.

I have added a comment that needs to be addressed before the PR is GTG.

[sebastiaanspeck]

Suggested change

	`blockdev --report /dev/sdX`
	- Get the size of a device in 512-byte sectors:
	`blockdev --getsz /dev/sdX`
	- Set read-only:
	`blockdev --setro /dev/sdX`
	- Set read-write:
	`blockdev --setrw /dev/sdX`
	- Flush buffers:
	`blockdev --flushbufs /dev/sdX`
	- Get the physical block size:
	`blockdev --getpbsz /dev/sdX`
	- Set the read-ahead value to 128 sectors:
	`blockdev --setra 128 /dev/sdX`
	`blockdev --report {{/dev/sdX}}`
	- Get the size of a device in 512-byte sectors:
	`blockdev --getsz {{/dev/sdX}}`
	- Set read-only:
	`blockdev --setro {{/dev/sdX}}`
	- Set read-write:
	`blockdev --setrw {{/dev/sdX}}`
	- Flush buffers:
	`blockdev --flushbufs {{/dev/sdX}}`
	- Get the physical block size:
	`blockdev --getpbsz {{/dev/sdX}}`
	- Set the read-ahead value to 128 sectors:
	`blockdev --setra 128 {{/dev/sdX}}`

[Managor]

Do the device paths need to be absolute or can they be relative?

[DarkMatter-999]

Yeah, the paths are required to be absolute.

[DarkMatter-999]

Thank you very much,

Fixed the formatting ✌️