adopt myst

run rst2myst, with minimal manual formatting fixes

docs/topic/requirements.md

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+(requirements)=
+
+# Server Requirements
+
+## Operating System
+
+We require using Ubuntu >=20.04 as the base operating system for your server.
+
+## Root access
+
+Full `root` access to this server is required. This might be via `sudo`
+(recommended) or by direct access to `root` (not recommended!)
+
+## External IP
+
+An external IP allows users on the internet to reach your JupyterHub. Most
+VPS / Cloud providers give you a public IP address along with your server. If
+you are hosting on a physical machine somewhere, talk to your system administrators
+about how to get HTTP traffic from the world into your server.
+
+## CPU / Memory / Disk Space
+
+See how to {ref}`howto/admin/resource-estimation`