docs: add link to transactions guide from nav bar

Fix #10143

Author: vkarpov15

docs/layout.pug

@@ -97,6 +97,8 @@ html(lang='en')
                 a.pure-menu-link(href="/docs/discriminators.html", class=outputUrl === '/docs/discriminators.html' ? 'selected' : '') Discriminators
               li.pure-menu-item.sub-item
                 a.pure-menu-link(href="/docs/plugins.html", class=outputUrl === '/docs/plugins.html' ? 'selected' : '') Plugins
+              li.pure-menu-item.sub-item
+                a.pure-menu-link(href="/docs/transactions.html", class=outputUrl === '/docs/transactions.html' ? 'selected' : '') Transactions
               li.pure-menu-item
                 a.pure-menu-link(href="/docs/api.html", class=outputUrl === '/docs/api.html' ? 'selected' : '') API
               li.pure-menu-item.sub-item