feat: add proposal for runtime graph image label

Signed-off-by: nullday <aseaday@hotmail.com>

docs/proposals/20220826-image-runtime-redistributed-metadata.md

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+# Add Runtime Redistributed Metadata To Image Metadata
+Authors:
+- [nullday](https://github.com/aseaday)
+
+## Summary
+
+The `envd` would add (runing graph metadata)[https://github.com/tensorchord/envd/blob/630ada172bdf876c3b749329fdbe284c108051f2/pkg/lang/ir/types.go#L70] would be encoded into a ASCII string and added to be image(OCI Spec) as a label. 
+
+## Motivation
+
+This proposal is part of effort to define what the artifact `envd` delivery and decoupling the phases of build and runing. It will be friendly for running a envd environment even at the absence of `build.env`.
+
+
+
+## Goals
+- Provide internal API:
+    - read runtime metadata
+    - write runtime metadata
+- `up` and `run` command doesn't need to interpret the `build.env`
+
+