chore(cli): Document how to install extra dependencies

Author: Zhe Yu

Makefile

@@ -1,11 +1,13 @@
 .PHONY: multitest
 
 EXTRA_LOCK_ARGS?=
+EXTRA_DEPS?=""
 DEFAULT_GROUPS=--group dev --group lsp --group mcp --group debug $(EXTRA_LOCK_ARGS)
 
 deps:
 	pdm lock $(DEFAULT_GROUPS) || pdm lock $(DEFAULT_GROUPS) --group legacy; \
 	pdm install
+	[ -z "$(EXTRA_DEPS)" ] || (pdm run python -m ensurepip && pdm run python -m pip install $(EXTRA_DEPS))
 
 test:
 	make deps; \

docs/CONTRIBUTING.md

@@ -40,6 +40,26 @@ You may also find it helpful to
 [enable logging](https://github.com/Davidyz/VectorCode/blob/main/docs/cli.md#debugging-and-diagnosing) 
 for the CLI when developing new features or working on fixes.
 
+### Local Dependencies
+
+Sometimes you want to run `make deps` that install non-default dependencies. The 
+`Makefile` provides easy ways to do that. 
+
+When you want to install a dependency group of VectorCode: 
+
+```bash 
+EXTRA_LOCK_ARGS="--group chroma0" make deps
+```
+
+When you want to install a library that is not declared in any of the dependency 
+groups (like `openai`):
+
+```bash 
+EXTRA_DEPS="openai\<2.0.0" make deps
+```
+
+Both environment variables apply to `make deps`, `make test` and `make coverage`.
+
 ### Database Connectors
 
 Please take a look at [the database documentation](../src/vectorcode/database/README.md),