crystal: add page (#2334)

pages/common/crystal.md

@@ -0,0 +1,23 @@
+# crystal
+
+> Tool for managing crystal source code.
+
+- Run a crystal file:
+
+`crystal {{path/to/file.cr}}`
+
+- Compile a file and all dependencies to a single executable:
+
+`crystal build {{path/to/file.cr}}`
+
+- Start a local interactive server for testing the language:
+
+`crystal play`
+
+- Create a project directory for a crystal application:
+
+`crystal init app {{application_name}}`
+
+- Display all help options:
+
+`crystal help`