Base: Add man page for blockdev utility

Base/usr/share/man/man8/blockdev.md

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+## Name
+
+blockdev - query block devices
+
+## Synopsis
+
+```**sh
+$ blockdev [options] <device>
+```
+
+## Description
+
+The `blockdev` command call ioctls on the given block device.
+
+## Options
+
+* `-s`, `--size`: Get disk size in bytes
+* `-b`, `--block-size`: Get block size in bytes
+
+## Examples
+
+```sh
+# Get disk size
+# blockdev -s /dev/hda
+863718912
+
+# Get block size
+# blockdev -b /dev/hda
+512
+```