added .editorconfig file with tab style and tab size information

https://editorconfig.org/

.editorconfig

@@ -0,0 +1,21 @@
+# EditorConfig
+# https://editorconfig.org/
+# https://editorconfig-specification.readthedocs.io/
+
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+# 4 space indentation
+[*.{h,cpp,html,css,js,conf,txt}]
+indent_style = tab
+indent_size = 4
+
+# Tab indentation (no size specified)
+[Makefile]
+indent_style = tab
+indent_size = 4