btrfs-progs: add basic .editorconfig

Not all contributors work on projects that use linux kernel coding
style. This commit adds a basic editorconfig [0] to assist contributors
with managing configuration.

[0]: https://editorconfig.org/

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: David Sterba <dsterba@suse.com>

.editorconfig

@@ -0,0 +1,10 @@
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+indent_style = tab
+indent_size = 8
+
+[*.py]
+indent_size = 4

.gitignore

@@ -65,6 +65,7 @@
 /cscope.in.out
 /cscope.po.out
 .*
+!.editorconfig
 
 /Documentation/Makefile
 /Documentation/*.html