tec: Add a .gitattributes file

This avoids to export files that aren't useful in production in Zip and
Tar archives. Note that `git archive` doesn't include submodules (i.e.
`lib/Minz`), so the archives don't have all the necessary files to work.
Hence, the only official way to install in production is still via `git
clone`.

Author: marienfressinaud

.gitattributes

@@ -0,0 +1,10 @@
+/.* export-ignore
+
+/docker export-ignore
+/tests export-ignore
+
+/composer.json export-ignore
+/composer.lock export-ignore
+
+/package-lock.json export-ignore
+/package.json export-ignore