Add become-a-member page

Remove changefreq and priority

website/thaliawebsite/sitemaps.py

@@ -3,11 +3,10 @@ from django.urls import reverse
 
 
 class StaticViewSitemap(sitemaps.Sitemap):
-    priority = 0.5
-    changefreq = 'daily'
 
     def items(self):
-        return ['index', 'become-active', 'sister-associations', 'contact']
+        return ['index', 'become-active', 'sister-associations',
+                'become-a-member', 'contact']
 
     def location(self, item):
         return reverse(item)