LICENSES: Add ISC license text

Add the full text of the ISC license to the kernel tree. It was copied
directly from:

   https://spdx.org/licenses/ISC.html

With the mention of "ISC" in the warranty disclaimer replaced with
"THE AUTHOR" as done in the ISC license headers used in the ath10k and
brcmfmac wifi drivers.

Cc: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

LICENSES/other/ISC

+Valid-License-Identifier: ISC
+SPDX-URL: https://spdx.org/licenses/ISC.html
+Usage-Guide:
+  To use the ISC License put the following SPDX tag/value pair into a
+  comment according to the placement guidelines in the licensing rules
+  documentation:
+    SPDX-License-Identifier: ISC
+License-Text:
+
+ISC License
+
+Copyright (c) <year> <copyright holders>
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.