Add Captcha configuration page (#1406)

* Add captcha page
* And warning to privacy block

content/en/admin/optional/captcha.md

@@ -0,0 +1,31 @@
+---
+title: Captcha
+description: Mitigating automated signup bots
+menu:
+  docs:
+    weight: 30
+    parent: admin-optional
+---
+
+As of Mastodon 4.2, using CAPTCHA technology is supported to help mitigate against bots signing up for new accounts.
+With CAPTCHA enabled, new registrations will be required to complete a challenge response as part of the e-mail verification process.
+
+![](/assets/captcha/user-view.png)
+
+{{< hint style="danger" >}}
+For some people, the use of a central CAPTCHA service may be a security and privacy concern.
+In addition, CAPTCHA can make the registration process significantly less accessible to some people.
+{{</ hint >}}
+
+Currently, hCaptcha is the only available provider supported by Mastodon.
+Other providers may be added in the future.
+
+## hCaptcha
+
+- Create a free hCaptcha account at [hcaptcha.com](https://www.hcaptcha.com)
+- After completing registration, generate a Site Key and Site Secret from the hCaptcha dashboard
+- Add the values to your Mastodon environment configuration as `HCAPTCHA_SITE_KEY` and `HCAPTCHA_SECRET_KEY`
+- Restart the Mastodon services running on your server
+- From the Mastodon web interface navigate to **Administration**  > **Server settings** > **Registrations** and check the box labled "Require new users to solve a CAPTCHA to confirm their account"
+
+![](/assets/captcha/admin-view.png)

content/en/admin/optional/object-storage.md

@@ -1,5 +1,5 @@
 ---
-title: Configuring object storage
+title: Object storage
 description: Serving user-uploaded files in Mastodon using external object storage
 menu:
   docs:

content/en/admin/optional/sso.md

@@ -2,7 +2,7 @@
 title: Single Sign On
 menu:
   docs:
-    weight: 30
+    weight: 40
     parent: admin-optional
 ---