Set Go toolchain and document license

Author: andrew

README.md

@@ -144,3 +144,7 @@ for profiling a single run.
 - Legal-path caps follow `licenses.LegalFileRoles`. Names such as
   `license.rs` are included; `THIRD_PARTY_LICENSES.txt` and `PATENTS` are not.
 - No `blame` or `diff A..B` subcommands yet.
+
+## License
+
+MIT

go.mod

@@ -2,6 +2,8 @@ module github.com/git-pkgs/git-spdx
 
 go 1.26.0
 
+toolchain go1.26.7
+
 require github.com/git-pkgs/licenses v0.7.1-0.20260906201711-03e6909a1db1
 
 require (