docs: Add Toolchain Package Manager Values (#3836)

* Update Docs to Add Toolchain Package Manager Values

* Hyperlink Valid package_manager Values

Author: 0xIchigo

docs/content/docs/references/anchor-toml.mdx

@@ -222,3 +222,19 @@ anchor_version = "0.31.1"    # `anchor-cli` version to use(requires `avm`)
 solana_version = "2.1.21"     # Solana version to use(applies to all Solana tools)
 package_manager = "yarn"     # JS package manager to use
 ```
+
+### package_manager
+
+The `package_manager` field indicates which package manager Anchor should use for all of its client and 
+workspace commands. [Valid values](https://github.com/solana-foundation/anchor/blob/cac1421e026ae27d06b52d849572cd8b5c1c5b8a/cli/src/config.rs#L309-L322) 
+include `npm`, `yarn`, `pnpm`, and `bun`.
+
+Anchor will default to `yarn`, if a value is not specified. Note values should be in lowercase, since
+values are deserialized with `serde(rename_all = "lowercase")`.
+
+Example:
+
+```toml
+[toolchain]
+package_manager = "pnpm"
+```