Add info about SDK azure-sdk-for-* checks and `SDK azure-powershell…

…` to `ci-fix` doc; Clean up markdownlint rules and `ci-fix` doc. (Azure#29311)

.markdownlint.jsonc

@@ -0,0 +1,35 @@
+{
+    "default": true,
+
+    // MD013 - Line length
+    // https://github.com/DavidAnson/markdownlint/blob/main/doc/md013.md
+    //
+    // "line_length" : 120:
+    // Allow lines of length 120 instead of the default 80. Keep in sync with guide lines .vscode/settings.json.
+    //
+    // "tables": false
+    // Do not include tables. Breaking a line in a table to meet the line length would add a line break in the table
+    // itself. We do not want that.
+    //
+    // "headings": false
+    // Do not include headings. One cannot break lines in headings, and we sometimes need long ones, e.g. for FAQs.
+    "MD013": { "line_length" : 120, "tables": false, "headings": false },
+
+    // MD025 - Multiple top-level headings in the same document
+    // https://github.com/DavidAnson/markdownlint/blob/main/doc/md025.md
+    //
+    // We sometimes prefer to have multiple top-level headings in the same document.
+    "MD025": false,
+
+    // MD033 - No inline HTML
+    // https://github.com/DavidAnson/markdownlint/blob/main/doc/md033.md
+    //
+    // We allow inline HTML as sometimes we need <br/> within table cells.
+    "MD033": false,
+
+    // MD034 - Bare URL used
+    // https://github.com/DavidAnson/markdownlint/blob/main/doc/md034.md
+    //
+    // We allow bare URLs e.g. to link to GitHub issues.
+    "MD034": false
+}

.vscode/settings.json

@@ -31,5 +31,10 @@
   "[typespec]": {
     "editor.defaultFormatter": "typespec.typespec-vscode",
     "editor.formatOnSave": true
-  }
+  },
+  "[markdown]": {
+    "editor.rulers": [
+        { "column": 120, "color": "#ff0000c0" }
+    ]
+},
 }