Add the MIT license (closes #14)

sneak chose MIT for keyfunc. LICENSE holds the standard MIT text with
the line "Copyright (c) 2026 sneak". The README's first paragraph and
its License section now name MIT, and the line for this issue leaves
the README TODO list.

Model: opus-5-5

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 sneak
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -1,11 +1,10 @@
 # keyfunc
 
-`keyfunc` is a Go command-line tool by [@sneak](https://sneak.berlin) — its
+`keyfunc` is an MIT-licensed Go command-line tool by
-license is not yet chosen
+[@sneak](https://sneak.berlin) that turns a BIP-39 mnemonic into SSH keys, age
-([#14](https://git.eeqj.de/sneak/keyfunc/issues/14)) — that turns a BIP-39
+identities and child mnemonics, each of which can be recreated from that
-mnemonic into SSH keys, age identities and child mnemonics, each of which can be
+mnemonic at any time. The same mnemonic, key type and index always give the same
-recreated from that mnemonic at any time. The same mnemonic, key type and index
+key.
-always give the same key.
 
 It uses the BIP-85 entropy deriver from `git.eeqj.de/sneak/secret/pkg/bip85` and
 takes the same steps as that repository's `agehd` package.
@@ -306,14 +305,11 @@ standard: most Makefile targets are thin shims over an executable in
 
 The open issues that stand between the tree and a 1.0 release:
 
-- [#14 Choose a license and add LICENSE](https://git.eeqj.de/sneak/keyfunc/issues/14)
 - [#15 Decide the Go module path before 1.0](https://git.eeqj.de/sneak/keyfunc/issues/15)
 
 ## License
 
-Not yet chosen. The license is the owner's decision, still open on the tracker
+MIT. The full text is in [`LICENSE`](LICENSE).
-([#14](https://git.eeqj.de/sneak/keyfunc/issues/14)); the `LICENSE` file is added
-when that issue is answered.
 
 ## Author