changelog: Use Git commit message style for Change Log fragments

It is more familiar to developers and prevents confusion between
requiring a Change Log fragment's subject line to end with period and
requiring a Git commit message's subject line not to end with a period.

.changelog/2406.breaking.md

@@ -1 +1 @@
-go/registry: Enable non-genesis runtime registrations by default.
+go/registry: Enable non-genesis runtime registrations by default

.changelog/2638.breaking.md

@@ -1 +1 @@
-Optionally require a deposit for registering a runtime.
+Optionally require a deposit for registering a runtime

.changelog/2642.breaking.1.md

@@ -1 +1 @@
-go/registry: Add explicit EntityID field to Runtime descriptors.
+go/registry: Add explicit EntityID field to Runtime descriptors

.changelog/2642.breaking.2.md

@@ -1,4 +1,4 @@
-go/staking: Add stateful stake accumulator.
+go/staking: Add stateful stake accumulator
 
 Previously there was no central place to account for all the parts that need
 to claim some part of an entity's stake which required approximations all

.changelog/2647.breaking.md

@@ -1,4 +1,4 @@
-staking: More reward for more signatures.
+staking: More reward for more signatures
 
 We're adjusting fee distribution and the block proposing staking reward to
 incentivize proposers to create blocks with more signatures.

.changelog/2662.internal.2.md

@@ -0,0 +1,4 @@
+changelog: Use Git commit message style for Change Log fragments
+
+For more details, see the description in [Change Log fragments](
+.changelog/README.md).

.changelog/README.md

@@ -1,7 +1,7 @@
 # Change Log fragments
 
 This directory collects Change Log fragments:
-short files that each contain a snippet of MarkDown formatted text that will
+short files that each contain a snippet of Markdown formatted text that will
 be assembled using [towncrier] to form the [Change Log] section for the next
 release.
 
@@ -14,36 +14,32 @@ _NOTE: This could be very different from the commit message and pull request
 description, which are a description of the change as relevant to the people
 working on the code itself._
 
-The description could use one of the following two formats:
+The description should follow the familiar [style of Git commit messages],
+i.e. a separate subject line giving the change's summary, followed by a more
+detailed explanation in the body.
 
-- One line change summary followed by an empty line and a more detailed
-  explanation in the body.
+In case of simpler descriptions, one can omit the description's body.
 
-  For example:
+_NOTE: Lines should be wrapped at 78 characters because Change Log fragments
+will be listed as bullets indented by 2 spaces so they should be 2 characters
+shorter than ordinary lines._
 
-  ```text
-  Remove staking-related roothash messages.
+An example:
 
-  There is no longer a plan to support direct manipulation of the staking
-  accounts from the runtimes in order to isolate the runtimes from corrupting
-  the consensus layer.
-
-  To reduce complexity, the staking-related roothash messages were removed.
-  The general roothash message mechanism stayed as-is since it may be useful
-  in the future, but any commits with non-empty messages are rejected for now.
-  ```
-
-- Shorter multi-line change description.
+```text
+Remove staking-related roothash messages
 
-  For example:
+There is no longer a plan to support direct manipulation of the staking
+accounts from the runtimes in order to isolate the runtimes from corrupting
+the consensus layer.
 
-  ```text
-  Add `oasis-node unsafe-reset` sub-command which resets the node back to a
-  freshly provisioned state, preserving any key material if it exists.
-  ```
+To reduce complexity, the staking-related roothash messages were removed.
+The general roothash message mechanism stayed as-is since it may be useful in
+the future, but any commits with non-empty messages are rejected for now.
+```
 
-_NOTE: Don't put links to issue(s)/pull request in your text as the
-[towncrier] tool will add them automatically._
+_NOTE: The [towncrier] tool will automatically augment each subject line with
+a link to an appropriate issue/pull request._
 
 ## File name
 
@@ -113,3 +109,4 @@ _NOTE: You can use any version for the preview, it doesn't really matter._
 [Change Log]: ../CHANGELOG.md
 [towncrier]: https://github.com/hawkowl/towncrier
 [Oasis Labs' towncrier fork]: https://github.com/oasislabs/towncrier
+[style of Git commit messages]: ../CONTRIBUTING.md#git-commit-messages