misc: rename install-git-hooks.go to add-git-hooks.go (#20144)

`go run` builds a manifest-less .exe, so Windows applies installer-
detection heuristics and requests admin privileges to programs that
contains "install", "setup", or "update". Rename to dodge that.

Updates #20133

Change-Id: I144d3fcb076d7a02e4a3eb9fd079ee022a035c76

Signed-off-by: Fernando Serboncini <fserb@tailscale.com>

misc/add-git-hooks.go

@@ -0,0 +1,21 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ignore
+
+// The add-git-hooks program installs git hooks by delegating to
+// githook.Install. See that function's doc for what it does.
+package main
+
+import (
+	"log"
+
+	"tailscale.com/misc/git_hook/githook"
+)
+
+func main() {
+	log.SetFlags(0)
+	if err := githook.Install(); err != nil {
+		log.Fatalf("add-git-hooks: %v", err)
+	}
+}