image: when using the new image build code, gzip ext4 images by default

[Christian Lamparter]

This is a comment on the patch:
>commit 87b668765e1e987aebef8cf0aae657569b631477
>Author: Felix Fietkau <nbd at nbd.name>
>Date:   Fri Jan 13 15:58:37 2017 +0100
>
>   image: when using the new image build code, gzip ext4 images by default
>
>   This reduces the amount of hacks in the makefile code.
>
>   Remove the apm821xx code to do the same - it was broken and left both
>   compressed and uncompressed images in $(BIN_DIR)

Let me explain that apm821xx code.

The uncompressed image was left in place because it allowed "easy install
method" by just using dd with the image on the original WD firmware. 
I refered to this method in the commit [0]:

>    The extracted/raw image can be directly installed on
>    the internal HDD via "dd if=img.ext4 of=/dev/sdX".
>
>    This can either be done in place with the stock MyBook Live
>    firmware via ssh. Or by removing the HDD and writing the image
>    with a different PC.
>
>    The the compressed images are useful for sysupgrade.

so there was some reason behind the uncompressed and compressed image.

Of course, back then the generated ext4 images where like 50-60 MiB.
So I'm fine with the change. But I would like to document the change
somewhere. Editing my wiki [1] is easy enough, but I would like to
move the article to LEDE's wiki. 

So how do I do that? 

[Actually, I want to know: If it is possible to add new articles to 
the wiki for supported devices in LEDE (not OpenWRT sadly) now - and
what format these articles should have.
As far as I can tell the current ToH just links to wiki.openwrt.org.
So I'm looking for a sample/template that just needs to be customized
for the different apm821xx targets.]

Regards,
Christian

[0] <https://git.lede-project.org/?p=source.git;a=commit;h=dc7efaefb53d4671893add07934839eb8d44934d>
[1] <https://github.com/chunkeey/apm82181-lede/wiki/Western-Digital-MyBook-Live>