trailer doc: emphasize the effect of configuration variables

The sentence does not mention the effect of configuration variables at
all, when they are actively used by default (unless --parse is
specified) to potentially add new trailers, without the user having to
always supply --trailer manually.

Signed-off-by: Linus Arver <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Linus Arver

Documentation/git-interpret-trailers.txt

@@ -34,9 +34,12 @@ This command reads commit messages from either the
 If `--parse` is specified, the output consists of the parsed trailers
 coming from the input, without influencing them with any command line
 options or configuration variables.
-Otherwise, this command applies the arguments passed using the
-`--trailer` option, if any, to each input file. The result is emitted on the
-standard output.
+
+Otherwise, this command applies `trailer.*` configuration variables
+(which could potentially add new trailers, as well as reposition them),
+as well as any command line arguments that can override configuration
+variables (such as `--trailer=...` which could also add new trailers),
+to each input file. The result is emitted on the standard output.
 
 This command can also operate on the output of linkgit:git-format-patch[1],
 which is more elaborate than a plain commit message. Namely, such output