Remove unused TrackReleaseBranches strategy listing from how-it-works

Mark TrackReleaseBranches as unused in configuration.md since technically it is an allowed value even though it's a noop.

docs/input/docs/learn/how-it-works.md

@@ -38,7 +38,8 @@ simply to show what happens if the check is true.
 
 Currently we have the following strategies:
 
-* `TaggedCommit` - Extracts version information from all tags on the branch which are valid, and not newer than the current commit.
+* `TaggedCommit` - Extracts version information from all tags on the branch which are valid,
+    and not newer than the current commit.
 * `VersionInBranchName` - Extracts version information from the
     branch name (e.g., `release/3.0.0` will find `3.0.0`)
 * `ConfiguredNextVersion` - Returns the version from the
@@ -48,8 +49,7 @@ Currently we have the following strategies:
 * `Fallback` - Always returns 0.0.0 and will be used for
     calculating the next version which is dependent on the increment strategy of
  the effected branch (e.g. on main the next version is 0.0.1 or on develop it is 0.1.0)
-* `TrackReleaseBranches` - TODO: Document this
-* `Mainline` - TODO: Document this
+* `Mainline` - Increments the version on every commit for branches configured with `mode: Mainline`
 
 Each strategy needs to return an instance of `BaseVersion` which has the
 following properties:

docs/input/docs/reference/configuration.md

@@ -955,7 +955,7 @@ Specifies which version strategy implementation (one ore more) will be used to d
 - ConfiguredNextVersion
 - MergeMessage
 - TaggedCommit
-- TrackReleaseBranches
+- TrackReleaseBranches (currently unused)
 - VersionInBranchName
 - Mainline