Add vendor operation to README (#7)

The vendor command was added in #5 but the README wasn't updated to
document it.

Author: andrew

README.md

@@ -4,7 +4,7 @@ A Go library that wraps package manager CLIs behind a common interface. Part of
 
 ## What it does
 
-Translates generic operations (install, add, remove, list, outdated, update) into the correct CLI commands for each package manager. Define what you want to do once, and the library figures out the right command for npm, bundler, cargo, go, or any other supported manager.
+Translates generic operations (install, add, remove, list, outdated, update, vendor) into the correct CLI commands for each package manager. Define what you want to do once, and the library figures out the right command for npm, bundler, cargo, go, or any other supported manager.
 
 ```go
 translator := managers.NewTranslator()
@@ -82,7 +82,7 @@ cmd, _ = translator.BuildCommand("bundler", "add", managers.CommandInput{
 | helm | helm | Chart.lock |
 | brew | homebrew | - |
 
-Most managers support: install, add, remove, list, outdated, update. Some managers (maven, gradle, sbt, lein) have limited CLI support for add/remove operations.
+Most managers support: install, add, remove, list, outdated, update. Some also support vendor and path. Some managers (maven, gradle, sbt, lein) have limited CLI support for add/remove operations.
 
 ## Installation
 
@@ -217,6 +217,7 @@ Built-in policies include AllowAllPolicy, DenyAllPolicy, and PackageBlocklistPol
 | `outdated` | Show packages with available updates |
 | `update` | Update dependencies |
 | `path` | Get filesystem path to installed package |
+| `vendor` | Copy dependencies into the project directory |
 
 ### Common flags
 
@@ -240,6 +241,17 @@ The library handles extracting clean paths from various output formats (JSON, li
 
 **Managers with path support:** npm, pnpm, yarn, bun, bundler, gem, pip, uv, poetry, conda, gomod, cargo, composer, brew, deno, nimble, opam, luarocks, conan, mix, shards, rebar3
 
+### Vendoring dependencies
+
+The `vendor` operation copies dependencies into the project directory for offline builds or source inspection:
+
+```go
+manager, _ := managers.Detect("/path/to/project")
+result, _ := manager.Vendor(ctx)
+```
+
+**Managers with vendor support:** gomod, cargo, bundler, pip, rebar3
+
 ### Escape hatch
 
 For manager-specific flags not covered by the common interface, use `Extra`: