html5validator: add page (#3558)

pages/common/html5validator.md

@@ -0,0 +1,32 @@
+# html5validator
+
+> A command line tool for testing HTML5 validity.
+> More information: <https://github.com/svenkreiss/html5validator>.
+
+- Validate a specific file:
+
+`html5validator {{path/to/file}}`
+
+- Validate all HTML files in a specific directory:
+
+`html5validator --root {{path/to/directory}}`
+
+- Show warnings as well as errors:
+
+`html5validator --show-warnings {{path/to/file}}`
+
+- Match multiple files using a glob pattern:
+
+`html5validator --root {{path/to/directory}} --match "{{*.html *.php}}"`
+
+- Ignore specific directory names:
+
+`html5validator --root {{path/to/directory}} --blacklist "{{node_modules vendor}}"`
+
+- Output the results in a specific format:
+
+`html5validator --format {{gnu|xml|json|text}} {{path/to/file}}`
+
+- Output the log at a specific verbosity level:
+
+`html5validator --root {{path/to/directory}} --log {{debug|info|warning}}`