Fix minor grammar error in gdb.texinfo
This fixes a small grammar issue in gdb.texinfo -- "additional" was
written where "additionally" is correct.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 15fa158..d2428ef 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -30552,7 +30552,7 @@
bottom in the order listed.
The names of the windows are the same as the ones given to the
-@code{focus} command (see below); additional, the @code{status}
+@code{focus} command (see below); additionally, the @code{status}
window can be specified. Note that, because it is of fixed height,
the weight assigned to the status window is of no importance. It is
conventional to use @samp{0} here.
