move contents of taskchampion repo to tc/

rust/POLICY.md

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+# Compatibility & deprecation
+
+Until TaskChampion reaches [v1.0.0](https://github.com/taskchampion/taskchampion/milestone/7), nothing is set in stone. That being said, we aim for the following:
+
+1. Major versions represent significant change and may be incompatible with previous major release.
+2. Minor versions are always backwards compatible and might add some new functionality.
+3. Patch versions should not introduce any new functionality and do what name implies — fix bugs.
+
+As there are no major releases yet, we do not support any older versions. Users are encouraged to use the latest release.
+
+## ABI policy
+
+1. We target stable `rustc`.
+2. TaskChampion will never upgrade any storage to a non-compatible version without explicit user's request.
+
+## API policy
+
+1. Deprecated features return a warning at least 1 minor version prior to being removed.
+
+    Example:
+
+    > If support of `--bar` is to be dropped in v2.0.0, we shall announce it in v1.9.0 at latest.
+
+2. We aim to issue a notice of newly added functionality when appropriate.
+
+    Example:
+
+    > "NOTICE: Since v1.1.0 you can use `--foo` in conjunction with `--bar`. Foobar!"
+
+3. TaskChampion always uses UTF-8.
+
+## Command-line interface
+
+Considered to be part of the API policy.
+
+## CLI exit codes
+
+- `0` - No errors, normal exit.
+- `1` - Generic error.
+- `2` - Never used to avoid conflicts with Bash.
+- `3` - Command-line Syntax Error.
+
+# Security
+
+See [SECURITY.md](./SECURITY.md).