Add comment-based help to tasks

We should add comment based help for all the tasks.

This is an example from DscResource.DocGenerator.

```
<#
.SYNOPSIS
This is a build task that generates conceptual help.

.PARAMETER ProjectPath
The root path to the project. Defaults to $BuildRoot.

.PARAMETER OutputDirectory
The base directory of all output. Defaults to folder 'output' relative to
the $BuildRoot.

.PARAMETER ProjectName
The project name. Defaults to the BaseName of the module manifest it finds
in either the folder 'source', 'src, or a folder with the same name as
the module.

.PARAMETER SourcePath
The path to the source folder name. Defaults to the same path where the
module manifest is found.

.PARAMETER ModuleVersion
The module version of the build module, e.g. '99.1.1-preview0001'. Defaults
to using the value from parent scope, if that is not available it defaults
to the property NuGetVersionV2 returned by GitVersion. If GitVersion is not
present, the parameter defaults to version '0.0.1'.

.PARAMETER BuildInfo
The build info object from ModuleBuilder. Defaults to an empty hashtable.

.NOTES
This is a build task that is primarily meant to be run by Invoke-Build but
wrapped by the Sampler project's build.ps1 (https://github.com/gaelcolas/Sampler).
#>
```

Start by locating all build task scripts in the repository and compare their current comment-based help with the DscResource.DocGenerator example in the issue. Add equivalent help sections for each task, documenting its purpose and parameters, then verify that every task has the requested help coverage.

Written by the indexing model from the issue text.