env: README: Expand examples of path syntax (#65972)

Author: mcsf

packages/env/README.md

@@ -499,7 +499,7 @@ Several types of strings can be passed into the `core`, `plugins`, `themes`, and
 | ----------------- | -------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
 | Relative path     | `.<path>\|~<path>`                           | `"./a/directory"`, `"../a/directory"`, `"~/a/directory"`                                                                           |
 | Absolute path     | `/<path>\|<letter>:\<path>`                  | `"/a/directory"`, `"C:\\a\\directory"`                                                                                             |
-| GitHub repository | `<owner>/<repo>[#<ref>]`                     | `"WordPress/WordPress"`, `"WordPress/gutenberg#trunk"`, if no branch is provided wp-env will fall back to the repos default branch |
+| GitHub repository | `<owner>/<repo>[/<path>][#<ref>]`                     | `"WordPress/WordPress"`, `"WordPress/gutenberg#trunk"`, `WordPress/themes/my-theme#my-branch`; if no branch is provided wp-env will fall back to the repo's default branch |
 | SSH repository    | `ssh://user@host/<owner>/<repo>.git[#<ref>]` | `"ssh://[email protected]/WordPress/WordPress.git"`                                                                                   |
 | ZIP File          | `http[s]://<host>/<path>.zip`                | `"https://wordpress.org/wordpress-5.4-beta2.zip"`                                                                                  |