docs: update README.template to include Cloud-only agents section

This commit adds a new section for Cloud-only agents in the README.template, enhancing the documentation to reflect recent changes in agent categorization. The new section utilizes the dynamic-categories function to display hosted agents.

Changes made:
- Added a "Cloud-only agents" section with dynamic categories for hosted agents.

No functional code changes were made.

Author: tobymarsden

README.template

@@ -14,6 +14,8 @@
     {{{dynamic-categories "interfaces" this}}}
 * [**Tools and MCP servers**](#tools-and-mcp-servers)
     {{{dynamic-categories "tools" this}}}
+* [**Cloud-only agents**](#cloud-only-agents)
+    {{{dynamic-categories "hosted-agents" this}}}
 * [Contributing](#contributing)
 
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