Add info about the "name" parameter in "boot_img_hdr" to the wiki

[z3ntu]

~~The name is empty for me, although it should be mromYYYYmmDD. Where do I set this? Also (more) documentation on the json (devices.json & device-specific manifest.json) files would be nice.~~ To see how I did it (anybody who finds this): https://github.com/z3ntu/android_device_fairphone_fp2/commit/65af28e00e475dc08489d2908eeeaac554710a38

To experienced people: There should be info about that in the wiki, as I had to debug the android app to find out why it wasn't detecting the recovery.