Fix issues with Build-Wiki and add Wiki documentation to CONTRIBUTING.md's Release section (#311)

Fixed some issues with `Build-Wiki`:

* Ensured that `Home.md` is not incorrectly categorized as deprecated.
* Fixed how we check for `platyPS` being installed.
* Fixed how we reference files in `Move-Item` to solve the issue when the file being moved is new.
* Added warning/reminder to run this under `PS7+` to avoid issue with how multi-line examples get formatted.

Also added Wiki updating instructions to the release section of `CONTRIBUTING.md`.

Author: HowardWolosky

CONTRIBUTING.md

@@ -37,6 +37,7 @@ Looking for information on how to use this module?  Head on over to [README.md](
     *   [Updating the CHANGELOG](#updating-the-changelog)
     *   [Adding a New Tag](#adding-a-new-tag)
     *   [Running the Release Build](#running-the-release-build)
+    *   [Updating the Wiki documentation](#updating-the-wiki-documentation)
 *   [Contributors](#contributors)
 *   [Legal and Licensing](#legal-and-licensing)
 
@@ -551,6 +552,41 @@ maintainer because it accesses internal services to sign the module files with M
 > Instructions for updating the `PowerShellGalleryApiKey` secret in the pipeline can be found in the
 > [internal Microsoft repo for this project](https://microsoft.visualstudio.com/Apps/_git/eng.powershellforgithub).
 
+#### Updating the Wiki Documentation
+
+The [Wiki](https://github.com/microsoft/PowerShellForGitHub/wiki) contains the full documentation
+for all exported commands from the module, thanks to [platyPS](https://github.com/PowerShell/platyPS).
+
+Every time a new release occurs, the Wiki should be updated to reflect any changes that occurred
+within the module.
+
+1. Ensure that you have cloned the Wiki:
+
+   ```
+   git clone https://github.com/microsoft/PowerShellForGitHub.wiki.git
+   ```
+
+2. Open a PowerShell 7+ console window (don't use Windows PowerShell as there's a platyPS bug
+   with that version regarding multi-line examples) and navigate to your Wiki clone.
+
+3. Run this command (assuming that you have a `PowerShellForGitHub` clone at the same level as your
+   Wiki clone):
+
+   ```powershell
+   ..\PowerShellForGitHub\build\scripts\Build-Wiki.ps1 -Path .\ -RemoveDeprecated -Verbose -Force
+   ```
+
+4. Verify the changes all make sense.  You will also need to manually copy the core content of
+   `PowerShellForGitHub.md` into `Home.md`.  For the time being, we are duplicating that content
+   in Home until such time as we have better content to put there.
+
+5. Commit the change and directly push it to the Wiki's `master` branch...no need to go through
+   a pull request for the Wiki changes.
+
+> This is not currently automated as part of the [Release pipeline](#running-the-release-build)
+> because I don't currently want to store any credentials/tokens with write access to the repo
+> in the pipeline.
+
 ----------
 
 ### Contributors

build/scripts/Build-Wiki.ps1

@@ -344,6 +344,11 @@ Set-StrictMode -Version 1.0
 
 $Path = Resolve-Path -Path $Path
 
+if ($PSVersionTable.PSVersion.Major -lt 7)
+{
+    Write-Warning 'It is recommended to run this with PowerShell 7+, as platyPS has a bug which doesn''t properly handle multi-line examples when run on older vesrions of PowerShell.'
+}
+
 $numSteps = 11
 $currentStep = 0
 $progressParams = @{
@@ -354,7 +359,7 @@ $progressParams = @{
 #######
 $currentStep++
 Write-Progress @progressParams -Status 'Ensuring PlatyPS installed' -PercentComplete (($currentStep / $numSteps) * 100)
-if ($null -eq (Get-Module -Name 'PlatyPS'))
+if ($null -eq (Get-Module -Name 'PlatyPS' -ListAvailable))
 {
     Write-Verbose -Message 'Installing PlatyPS Module'
     Install-PackageProvider -Name NuGet -MinimumVersion 2.8.5.201 -Scope CurrentUser -Force -Verbose:$false | Out-Null
@@ -377,6 +382,7 @@ $moduleRootPageFileName = "$ModuleName.md"
 # files that should be _removed_ from the Wiki due to rename/removal of exports.
 $tempFolder = Join-Path -Path $env:TEMP -ChildPath ([Guid]::NewGuid().Guid)
 New-Item -Path $tempFolder -ItemType Directory | Out-Null
+Write-Verbose -Message "Working from temp location: $tempFolder"
 
 #######
 $currentStep++
@@ -475,7 +481,7 @@ foreach ($file in $currentFiles)
     $content = Get-Content -Path $file -Raw -Encoding utf8
     if (($content -match $generatedMarker) -and
         ($file.BaseName -notin $modulePages) -and
-        ($file.Name -ne $moduleRootPageFileName))
+        ($file.Name -notin ($moduleRootPageFileName, 'Home.md')))
     {
         $deprecatedFiles += $file
     }
@@ -508,7 +514,7 @@ Write-Progress @progressParams -Status "Moving generated content to final destin
 $files = Get-ChildItem -Path $tempFolder
 foreach ($file in $files)
 {
-    Move-Item -Path $file -Destination $Path -Force:$Force.IsPresent
+    Move-Item -Path $file.FullName -Destination $Path -Force:$Force.IsPresent
 }
 
 Remove-Item -Path $tempFolder -Recurse -Force