add editorconfig

I have included some common rules I've see applied in ::gentoo.
Please help to make a complete list OR remove the ones that you think
are too restrictive, but I do like to have metadata.xml formatted the same.
... yea, I know that up until now I used to use spaces in metadata.xml

Signed-off-by: Maciej Barć <xgqt@protonmail.com>

.editorconfig

@@ -0,0 +1,16 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+tab_width = 4
+
+[*.ebuild]
+indent_style = tab
+
+[metadata.xml]
+indent_style = tab
+
+[repositories.xml]
+indent_style = space
+tab_width = 2