documentation: Update installation

docs/installation/clients/specification.md

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+# Specification
+
+## Profile
+
+Profile defines a sing-box configuration with metadata in a GUI client.
+
+## Profile Types
+
+### Local
+
+Create a empty configuration or import from a local file.
+
+### iCloud (on Apple platforms)
+
+Create a new configuration or use an existing configuration on iCloud. 
+
+### Remote
+
+Use a remote URL as the configuration source, with HTTP basic authentication and automatic update support.
+
+#### URL specification
+
+```
+sing-box://import-remote-profile?url=urlEncodedURL#urlEncodedName
+```