Add short section about installation, add license file

Author: ad-si

license.txt

@@ -0,0 +1,15 @@
+ISC License
+
+Copyright (c) 2022 Adrian Sieber
+
+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.

readme.md

@@ -57,3 +57,9 @@ a leading digit is encoded as `XXZ[0-9]`.
 
 If the optional double underscore encoding is enabled,
 double underscores are encoded as `XXRXXR`.
+
+
+## Installation
+
+The code is not yet available via common package managers.
+Please copy the code into your project for the time being.