Improve docs about releasing new crate versions

contrib/how_to_release.md

@@ -2,16 +2,45 @@
 
 ## General
 
-* When releasing a pre-release version, make sure other crates are updated to
+* `ruma-identifiers-validation` and the `-macros` crates don't get their own
-  depend on it, with an exact version requirement (`=x.y.z-tag`)
+  release commit or tag since they are internal packages.
-* When releasing a regular version, make sure other crates are updated to depend
+* Macro crates are versioned identically to their "parent" crate and need to be
-  on it, with a regular (same as caret / `^`) version requirement (`x.y.z`)
+  released before the parent crate.
-* Macro crates are versioned identically to their "parent" crate and are exempt
+* `ruma-identifiers-validation` is released before `ruma-identifiers-macros`
-  from the rule above: Dependencies from the parent crate to the macro crate
+  and `ruma-identifiers`.
-  (for re-exporting) should always use exact version requirements. Whenever a
+
-  crate with an associated macro crate should get a new release, release a new
+## Creating a release commit
-  version of the macro crate with the same number first, even if there were no
+
-  changes in the macro code.
+*To be automated in the future, see https://github.com/ruma/ruma/issues/452.*
+
+Update `Cargo.toml` of the relevant package, and update the dependency on this
+package in other crates in the workspace (if applicable):
+
+* When doing a prerelease (e.g. `0.10.0-beta.1`), depend on it with an exact
+  version requirement (`version = "=0.10.0-beta.1`)
+  * Macro crate dependencies always use an exact version requirement, even for
+    final releases.
+  * Otherwise, use `version = "x.y.z"`.
+
+Update the `CHANGELOG.md` of the relevant package.
+
+* If there is already a section for the version to be released, remove the
+  `(unreleased)` from its title.
+  * Otherwise, change the `[unreleased]` section title to the version being
+    released.
+
+Finally, commit these changes as `Release {crate} {version}`.
+
+## Publishing to crates.io and creating a release tag
+
+*Note: only do this for final release, i.e. not alpha or beta releases, and not
+for `ruma-identifiers-validation` or one of the macro crates.*
+
+All you have to do is run the corresponding `xtask` command:
+
+```
+cargo xtask release {crate}
+```
 
 ## Dependencies