Add an installation instructions section to the README

Added an Installation section to README.md:8 covering go install and build-from-source, with a note that the examples use go run ./cmd/git-sync and how to swap in the installed binary.
Swapped all go run ./cmd/git-sync invocations in the README for git-sync and dropped the now-unneeded swap note from the Installation section.
Context
- Current git status: On branch main Your branch is up to date with 'origin/main'.
Changes not staged for commit: (use "git add <file>..." to update what will be committed) (use "git restore <file>..." to discard changes in working directory) modified: README.md
no changes added to commit (use "git add" and/or "git commit -a")
- Current git diff (staged and unstaged changes): diff --git c/README.md w/README.md
index 1196da1..e179c55 100644
--- c/README.md
+++ w/README.md
@@ -31,10 +31,30 @@ Additional commands (
bootstrap,probe,fetch) and advanced flags are avail
git-sync is also a Go library. Use entire.io/entire/gitsync for the stable embedding surface (Probe, Plan, Sync, Replicate, typed results, auth and HTTP injection). entire.io/entire/gitsync/unstable exposes advanced controls (Bootstrap, Fetch, batching knobs, heap measurement) and is not stable.
+## Installation
+
+Requires Go 1.26 or newer.
+
+Install the latest release with go install:
+
+bash +go install entire.io/entire/gitsync/cmd/git-sync@latest +
+
+This drops a git-sync binary into $(go env GOPATH)/bin. Make sure that directory is on your PATH.
+
+Or build from source:
+
+bash +git clone https://github.com/entireio/gitsync.git +cd gitsync +go build -o git-sync ./cmd/git-sync +
+