.editorconfig: extend rules to .yml and .md files

Added a rule for YAML files
    Ensure we all use the same settings
    Enabled trim_trailing_whitespace for all files, except Markdown ones
    Removed unused comments
    Some of them are even irrelevant

.editorconfig

@@ -1,17 +1,21 @@
-# top-most EditorConfig file
 root = true
 
-# Unix-style newlines with a newline ending every file
 [*]
 charset = utf-8
 end_of_line = lf
 insert_final_newline = true
+trim_trailing_whitespace = true
 
-# Matches multiple files with brace expansion notation
 [*.v]
 indent_style = tab
 indent_size = 4
-trim_trailing_whitespace = true
+
+[*.{yml,yaml}]
+indent_style = space
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false
 
 [Makefile]
 indent_style = tab