.editorconfig: add

This allows IDEs that support this standard to automatically use the
correct formatting options.

Closes #18409

.editorconfig

@@ -0,0 +1,18 @@
+# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+#
+# SPDX-License-Identifier: curl
+
+root = true
+
+[*]
+charset = utf-8
+insert_final_newline = true
+indent_style = space
+trim_trailing_whitespace = true
+
+[*.{c,h}]
+indent_size = 2
+max_line_length = 79
+
+[*.{pl,pm}]
+indent_size = 4

Makefile.am

@@ -79,7 +79,7 @@ PLAN9_DIST = plan9/include/mkfile \
  plan9/src/mkfile.inc             \
  plan9/src/mkfile
 
-EXTRA_DIST = CHANGES.md COPYING RELEASE-NOTES Dockerfile \
+EXTRA_DIST = CHANGES.md COPYING RELEASE-NOTES Dockerfile .editorconfig \
  $(CMAKE_DIST) $(VC_DIST) $(WINBUILD_DIST) $(PLAN9_DIST)
 
 DISTCLEANFILES = buildinfo.txt