Make wording re manual flag more explicit (haskell#10781)

* Update cabal-package-description-file.rst

make the documentation around the ``manual`` flag a little clearer

* Update cabal-package-description-file.rst

update description of manual flag

* Update cabal-package-description-file.rst - whitespace

* Update doc/cabal-package-description-file.rst

Co-authored-by: Javier Sagredo <[email protected]>

---------

Co-authored-by: Javier Sagredo <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: 3 people

doc/cabal-package-description-file.rst

@@ -2462,10 +2462,11 @@ Configuration Flags
     :default: ``False``
     :since: 1.6
 
-    By default, Cabal will first try to satisfy dependencies with the
-    default flag value and then, if that is not possible, with the
-    negated value. However, if the flag is manual, then the default
-    value (which can be overridden by commandline flags) will be used.
+      By default, Cabal tries to resolve dependencies using the flag's ``default`` value.
+      If that fails, it tries again with the negated default value. However, if the flag is
+      marked as ``manual``, Cabal will only use the default value and will not retry
+      with the negated default. Note that the default value can still be overridden
+      using command-line flags.
 
 .. _conditional-blocks: