Minor documentation rephrasing

Author: pont-us

docs/start.md

@@ -9,9 +9,10 @@ version from PyPI:
 pip install zappend
 ```
 
-You can also install `zappend[dev]` to also install development dependencies,
-`zappend[doc]` to also install documentation-building dependencies, or
-`zappend[dev,doc]` for both.
+You can replace `zappend` with `zappend[dev]` in the above command to also
+install development dependencies, with `zappend[doc]` to also install
+documentation-building dependencies, or with `zappend[dev,doc]` to get both
+additional dependency sets.
 
 To install the latest version for development, clone the
 [repository](https://github.com/bcdev/zappend), and with the repository’s root