doc: improve neomake-makers-processing/neomake-makers-mapexpr

doc/neomake.txt

@@ -149,11 +149,11 @@ run on an whole project rather than a specific file.
 
                                                    *neomake-makers-processing*
                                                       *neomake-makers-mapexpr*
-You can define two optional properties on a maker object to process the maker
-output: `mapexpr` is applied to the maker output before any processing, and
-`postprocess` is applied to the quickfix or location list entry.
+You can define two optional properties on a maker object to process its
+output: `mapexpr` is applied to the maker's output before any processing, and
+`postprocess` is applied to each of the quickfix or location list entries.
 
-The `mapexpr` property will be passed directly into |map()| as the expr
+The `mapexpr` property will be passed directly into |map()| as the `expr`
 argument like so: >
     call map(lines, maker.mapexpr)
 <where `lines` contains the maker output.
@@ -568,4 +568,4 @@ Here are some tips to develop the 'errorformat' setting for makers:
    currently removed by default in Neomake, but that is supposed to change
    likely: it is better to ignore them through the |'errorformat'| already.
 
-vim: ft=help tw=78 isk+=<,>,\:
+vim: ft=help tw=78 isk+=<,>,\:,-