Re #6944 Alternative approach to docs for --force-dirty flag

Author: mpilgrem

doc/commands/build_command.md

@@ -339,23 +339,22 @@ Default: Disabled
 
 A package that is unchanged from when it was last built by Stack is said to be
 _clean_ and _dirty_ means the opposite. Set the flag to force the rebuild of
-packages that could, in principle, be dirty (such as
-[project packages](../configure/yaml/project.md#packages) or local file
-path [extra-deps](../configure/yaml/project.md#extra-deps)) even when it does
-not seem necessary based on file dirtiness.
+local packages ([project packages](../configure/yaml/project.md#packages) or
+local file path [extra-deps](../configure/yaml/project.md#extra-deps)) even when
+it does not seem necessary based on file cleanliness.
 
 !!! note
 
-    The flag `--force-dirty` has no effect if packages to be built do not
-    include any that could, in principle, be dirty. Packages that are deemed
-    immutable (unchanging) by Stack cannot, in principle, be dirty.
+    The flag `--force-dirty` has no effect if no local packages would be built.
+    Packages that Stack deems immutable (unchanging) cannot, in principle, be
+    dirty.
 
     There may be circumstances in which you wish Stack to rebuild an installed
     Haskell package (one registered in the relevant package database) that is
-    deemed immutable. For example, if that package has a dependency on a C
-    library that has, in fact, changed since the package was registered. To
-    cause Stack to try to rebuild such a package, first unregister it from the
-    package database by commanding:
+    deemed immutable. For example, if it has a dependency on a C library that
+    has, in fact, changed since the package was registered. To cause Stack to
+    try to rebuild such a package, first unregister it from the package database
+    by commanding:
 
     ~~~text
     stack exec -- ghc-pkg unregister --force <package>