README/editorconfig: Add .editorconfig to improve editing consistency.

Add small section in README to document the benefits.

.editorconfig

@@ -0,0 +1,26 @@
+# See https://editorconfig.org
+
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+indent_size = 4
+indent_style = space
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.{py,pyi}]
+max_line_length = 88
+
+[*.{md,yaml,yml}]
+indent_size = 2
+
+[Makefile]
+indent_style = tab
+
+[*.diff]
+trim_trailing_whitespace = false
+
+[.git/*]
+trim_trailing_whitespace = false

README.md

@@ -494,6 +494,15 @@ If using make with pip, running `make` will ensure the development environment
 is up to date with the specified dependencies, useful after fetching from git
 and rebasing.
 
+#### Editing the source
+
+Pick your favorite text editor or development environment!
+
+The source includes an `.editorconfig` file which enables many editors to
+automatically configure themselves to produce files which meet the minimum
+requirements for the project. See https://editorconfig.org for editor support;
+note that some may require plugins if you wish to use this feature.
+
 #### Passing linters and automated tests
 
 The linters and automated tests (pytest) are run in CI (GitHub Actions) when