git: show hidden tracked files

The hidden files are not considered because of the first rule in
.gitignore file.

In order to see changes in the hidden tracked files,
they are added in .gitignore as explicit include rules.

The derivatives of the first level files are also shown.
Example: .mailmap.rej

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>

.gitignore

@@ -1,5 +1,10 @@
 # ignore hidden files
 .*
+# except the tracked ones and derivatives
+!.ci/
+!.github/
+!.gitignore*
+!.mailmap*
 
 # ignore generated documentation tables
 doc/guides/nics/overview_table.txt