grip: add page (#6946)

pages/common/grip.md

@@ -0,0 +1,20 @@
+# grip
+
+> Preview GitHub-flavoured Markdown files locally.
+> More information: <https://github.com/joeyespo/grip>.
+
+- Start the server and serve the rendered `README` file of a current directory:
+
+`grip`
+
+- Start the server and serve a specific Markdown file:
+
+`grip {{path/to/file.md}}`
+
+- Start the server and open the `README` file of the current directory in the browser:
+
+`grip --browser`
+
+- Start the server in the specified port and serve the rendered `README` file of the current directory:
+
+`grip {{port}}`