📝 Inline Ruby string expansion documentation

(Forgot to update Mixins documentation)

docs/CeedlingPacket.md

@@ -2015,6 +2015,8 @@ Each subsection is optional.
  section) and as a lookup name among Ceedling’s built-in mixins
  (currently none).
 
+ Enabled entries support [inline Ruby string expansion][inline-ruby-string-expansion].
+
  **Default**: `[]`
 
 * `:load_paths`
@@ -2029,6 +2031,8 @@ Each subsection is optional.
 
  Both mixin names in the `:enabled` list (above) and on the command
  line via `--mixin` flag use this list of load paths for searches.
+
+ Load paths entries support [inline Ruby string expansion][inline-ruby-string-expansion].
 
  **Default**: `[]`
 
@@ -2185,6 +2189,7 @@ string generated by a command line utility.
 
 #### Project file sections that offer inline Ruby string expansion
 
+* `:mixins`
 * `:environment`
 * `:paths` plus any second tier configuration key name ending in `_path` or
  `_paths`
@@ -2421,6 +2426,8 @@ This section of a project configuration file is documented in the
 * A `:mixins` section in a Ceedling configuration is entirely filtered out of
  the resulting configuration. That is, it is unavailable for use by plugins
  and will not be present in any output from `ceedling dumpconfig`.
+* A `:mixins` section supports [inline Ruby string expansion][inline-ruby-string-expansion].
+ See the full documetation on Mixins for details.
 
 ## `:test_build` Configuring a test build