docs: Create path.Clean documentation

Related to #9005

content/en/functions/path.Clean.md

@@ -0,0 +1,26 @@
+---
+title: path.Clean
+description: Replaces path separators with slashes (`/`) and removes extraneous separators.
+date: 2021-10-08
+# publishdate: 2018-11-28
+# lastmod: 2018-11-28
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [path]
+signature: ["path.Clean PATH"]
+---
+
+`path.Clean` replaces path separators with slashes (`/`) and removes extraneous separators, including trailing separators.
+
+```
+{{ path.Clean "foo//bar" }} → "foo/bar"
+{{ path.Clean "/foo/bar/" }} → "/foo/bar"
+```
+
+On a Windows system, if `.File.Path` is `foo\bar.md`, then:
+
+```
+{{ path.Clean .File.Path }} → "foo/bar.md"
+```