Add release checklist (#115)

This PR adds a release checklist to ensure we properly release the
litep2p crate on crates.io.

Ideally, we'd need to switch to a crates.io release schedule and update
substrate soon.
Some developers complained a few weeks ago about the litep2p version not
being pinned in the polkadot release.
At the same time, when a polkadot create is release on crates.io, any
github dependency is replaced with the latest on crates.io.

cc @paritytech/networking

Signed-off-by: Alexandru Vasile <[email protected]>

RELEASING.md

@@ -0,0 +1,64 @@
+# Release Checklist
+
+These steps assume that you've checked out the Litep2p repository and are in the root directory of it.
+
+We also assume that ongoing work done is being merged directly to the `master` branch.
+
+1. Ensure that everything you'd like to see released is on the `master` branch.
+
+2. Create a release branch off `master`, for example `release-v0.3.0`. Decide how far the version needs to be bumped based
+   on the changes to date. If unsure what to bump the version to (e.g. is it a major, minor or patch release), check with the
+   Parity Networking team.
+
+3. Bump the crate version in the root `Cargo.toml` to whatever was decided in step 2 (basically a find and replace from old version
+   to new version in this file should do the trick).
+
+4. Ensure the `Cargo.lock` file is up to date.
+
+    ```bash
+    cargo generate-lockfile
+    ```
+
+5. Update `CHANGELOG.md` to reflect the difference between this release and the last. If you're unsure of
+   what to add, check with the Networking team. See the `CHANGELOG.md` file for details of the format it follows.
+
+   First, if there have been any significant changes, add a description of those changes to the top of the
+   changelog entry for this release.
+
+   Next, mention any merged PRs between releases.
+
+6. Commit any of the above changes to the release branch and open a PR in GitHub with a base of `master`.
+
+7. Once the branch has been reviewed and passes CI, merge it.
+
+8. Now, we're ready to publish the release to crates.io.
+
+    1. Checkout `master`, ensuring we're looking at that latest merge (`git pull`).
+
+        ```bash
+        git checkout master && git pull
+        ```
+
+    2. Perform a final sanity check that everything looks ok.
+
+        ```bash
+        cargo test --all-targets
+        ```
+
+    3. Run the following command to publish the crate on crates.io:
+
+        ```bash
+        cargo publish
+        ```
+
+9. If the release was successful, tag the commit that we released in the `master` branch with the
+   version that we just released, for example:
+
+    ```bash
+    git tag -s v0.3.0 # use the version number you've just published to crates.io, not this one
+    git push --tags
+    ```
+
+   Once this is pushed, go along to [the releases page on GitHub](https://github.com/paritytech/litep2p/releases)
+   and draft a new release which points to the tag you just pushed to `master` above. Copy the changelog comments
+   for the current release into the release description.