added conf settings for running grav in sud dir, on nginx

nginx.conf

@@ -26,6 +26,21 @@ http {
 		if (!-e $request_filename){ rewrite ^(.*)$ /index.php last; }
 	}
 
+	# if you want grav in a sub-directory of your main site 
+	# (for example, example.com/mygrav) then you need this rewrite:
+        location /mygrav {
+            index  index.php;
+            if (!-e $request_filename){ rewrite ^(.*)$ /mygrav/$2 last; }
+            try_files $uri $uri/ /index.php?$args;
+        }
+
+	# if using grav in a sub-directory of your site,
+	# prepend the actual path to each location
+	# for example: /mygrav/images
+	# and: /mygrav/user
+	# and: /mygrav/cache
+	# and so on
+ 
 	location /images/ {
 		# Serve images as static
 	}