Move the Go module to sneak.berlin/go/keyfunc (closes #15)

REPO_POLICIES.md sets the Go module root to sneak.berlin/go/<name>.
go.mod, every import of the old path and the -X path in the Makefile
LDFLAGS now use sneak.berlin/go/keyfunc; make fmt moved those imports
to their new place in the sort order. The old path keeps no alias. The
README gives the go install line next to the build from a clone and
drops this issue from its TODO list.

Model: opus-5-5

README.md

@@ -16,7 +16,13 @@ them, and `keyfunc mnemonic ...` for child mnemonics derived from the main one.
 
 ## Getting Started
 
-Build from a clone and run the binary:
+Install with Go:
+
+```
+go install sneak.berlin/go/keyfunc/cmd/keyfunc@latest
+```
+
+Or build from a clone and run the binary:
 
 ```
 git clone git@git.eeqj.de:sneak/keyfunc.git
@@ -307,7 +313,6 @@ 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