doc lz4 -1 changed to lz4 -l

[ProBackup-nl]

lz4 -l is necessary for Linux kernel boot compatibility, a separate branch and patch has already been pull request for that change in code. This patch also updates the documentation for that change. And it includes a table with an example to show the real life trade offs for extraction time, creation time and size based on an example.

[jsmeix]

I will merge this one when I merge
#1235

[gdha]

@jsmeix @ProBackup-nl Perhaps wait a few days to merge this pull request as it was already added some days ago. I want to be sure it is a valid one.

[jsmeix]

@gdha
the actual change is in
#1235
and I think this cannot go wrong because
the lz4 initrd compression was newly added
by @ProBackup-nl and when he now changes it
there cannot be regressions.

[ProBackup-nl]

@gdha The was insufficient testing in my initial commit. I only tested writing. I skipped the part to test that I could actually boot from is. Any suggestions what else I could/should test?

[jsmeix]

According to
#1236 (comment)
I will wait until Thursday and merge this one together with
#1235
on Thursday if there are no objections from @gdha

[jsmeix]

For some background information see
#1218 (comment)