feat: create prompt from file

src/Model/Completion/Prompt/PromptTemplate.php

@@ -59,6 +59,23 @@ public static function from(string $template): self
         return new self($template, []);
     }
 
+    /**
+     * Create a new prompt from the given file.
+     *
+     * <code>
+     *     $template = PromptTemplate::fromFile("/path/to/file.txt");
+     * </code>
+     */
+    public static function fromFile(string $path): self
+    {
+        $content = file_get_contents($path);
+        if ($content === false) {
+            throw new \RuntimeException("Could not read the file at path: {$path}");
+        }
+
+        return new self($content, []);
+    }
+
     /**
      * Format the prompt with the given values.
      * The values should be an associative array where the key is the placeholder