Add Prettier.md to document compatibility issues (fixes #410).

doc/Prettier.md

@@ -0,0 +1,23 @@
+# Using markdownlint with Prettier
+
+[`Prettier`](https://prettier.io) is a popular code formatter. For the most part,
+it works seamlessly with `markdownlint`. Special situations are documented
+below.
+
+## List item indentation
+
+The default settings of `markdownlint` and `Prettier` are compatible and don't
+result in any linting violations. If `Prettier` is used with `--tab-width` set
+to `4`, the following `markdownlint` configuration can be used:
+
+```json
+{
+  "MD007": {
+    "indent": 4
+  },
+  "MD030": {
+    "ul_single": 3,
+    "ul_multi": 3
+  }
+}
+```

doc/Rules.md

@@ -329,6 +329,8 @@ issue for multi-markdown parsers, which require 4-space indents. More informatio
 <https://cirosantilli.com/markdown-style-guide#indentation-of-content-inside-lists>
 and <http://support.markedapp.com/discussions/problems/21-sub-lists-not-indenting>.
 
+Note: See [Prettier.md](Prettier.md) for compatibility information.
+
 <a name="md009"></a>
 
 ## MD009 - Trailing spaces
@@ -1183,6 +1185,8 @@ for your selected document style.
 
 Rationale: Violations of this rule can lead to improperly rendered content.
 
+Note: See [Prettier.md](Prettier.md) for compatibility information.
+
 <a name="md031"></a>
 
 ## MD031 - Fenced code blocks should be surrounded by blank lines

test/markdownlint-test.js

@@ -80,6 +80,7 @@ test.cb("projectFilesNoInlineConfig", (t) => {
       "README.md",
       "CONTRIBUTING.md",
       "doc/CustomRules.md",
+      "doc/Prettier.md",
       "helpers/README.md"
     ],
     "noInlineConfig": true,
@@ -94,6 +95,7 @@ test.cb("projectFilesNoInlineConfig", (t) => {
       "README.md": [],
       "CONTRIBUTING.md": [],
       "doc/CustomRules.md": [],
+      "doc/Prettier.md": [],
       "helpers/README.md": []
     };
     t.deepEqual(actual, expected, "Issue(s) with project files.");