docs: add mock-rpmautospec to prerequisites in README (#475)

Author: liunan-ms

README.md

@@ -17,9 +17,9 @@ Among other functions, it supports:
 
 1. Install `golang` and other prerequisites via your system's package manager, e.g.:
    ```
-   dnf install -y golang mock dnf-utils
+   dnf install -y golang mock dnf-utils mock-rpmautospec
    ```
-
+   - `mock-rpmautospec` plugin hooks `rpmautospec` into mock's build lifecycle. It pulls `rpmautospec` as a dependency which processes `%autorelease` and `%autochangelog` macros in spec files.
 1. Ensure you are logged into your GitHub EMU account (`<alias>_microsoft`) via the GitHub CLI. If
    you are authenticated via multiple identities, you may need to use `gh auth switch` to switch
    your active identity. Also ensure that you have configured `git` to use `gh` for authenticating.