LICENSES: Missing ISC text & possibly a category ("Not recommended" vs. "Preferred licenses")

[RafaÅ MiÅecki]

Hi,

Due to some maintainers *preferring* BSD-compatible license for DTS
files [0], I was writing mine using ISC. I had no very special reason
for it: I was choosing between BSD-2-Clause, MIT and ISC. I've chosen
ISC as I read about its "removal of language deemed unnecessary".

I took a moment to look at the new SPDX thing and noticed that:
1) File license-rules.rst provides "LICENSES/other/ISC" as an example
2) License file LICENSES/other/ISC doesn't exist
3) ISC is listed as an *example* under the "Not recommended licenses"

First of all, as ISC is used by some files in the Linux kernel, I
think it's worth adding to the LICENSE/*/ISC.

Secondly, it isn't 100% clear to me if ISC is preferred or not
recommended. File license-rules.rst suggests the later by listing it
as an example for "Not recommended". It's just an example though, so
I'm not 100% sure without seeing it in either: "preferred" or "other"
directories. Also if anyone finds it "Not recommended", can we get a
short explanation why is it so, please?

[0] https://lkml.org/lkml/2016/5/4/707

-- 
RafaÅ