[move] Add example of user code organized into multiple packages

sui_programmability/examples/multi_package/README.md

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+An example of how to structure your code to include another user-level package as a dependency.
+
+Make sure that the dependency name (in this example DepPackage in main_package/Move.toml file's
+`[dependencies]` section) is the same as the name of the package (in dep_package/Move.toml file's
+`[package]` section).

sui_programmability/examples/multi_package/dep_package/Move.toml

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+[package]
+name = "DepPackage"
+version = "0.0.1"
+
+[dependencies]
+Sui = { local = "../../../../crates/sui-framework" }
+
+[addresses]
+dep_package = "0x0"

sui_programmability/examples/multi_package/dep_package/sources/dep_module.move

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+module dep_package::dep_module {
+
+    public fun foo(): u64 {
+        42
+    }
+
+}

sui_programmability/examples/multi_package/main_package/Move.toml

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+[package]
+name = "MainPackage"
+version = "0.0.1"
+
+[dependencies]
+Sui = { local = "../../../../crates/sui-framework" }
+DepPackage = { local = "../dep_package" }
+
+[addresses]
+main_package = "0x0"

sui_programmability/examples/multi_package/main_package/sources/main_module.move

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+module main_package::main_module {
+    use dep_package::dep_module;
+
+    fun foo(): u64 {
+        dep_module::foo()
+    }
+
+}