Break out KSP install detection to its own page

Author: drewcassidy

KSPCommon.targets

@@ -108,7 +108,7 @@
     <Error Text="KSPBuildTools was unable to find a KSP installation. Please set the ReferencePath or KSPBT_GameRoot property
                  in your csproj.user file to a valid KSP installation directory (the one with GameData in it)
 
-                 See https://kspbuildtools.readthedocs.io/en/latest/msbuild/getting-started.html#locating-your-ksp-install for more information"
+                 See https://kspbuildtools.readthedocs.io/en/latest/msbuild/ksp-install.html for more information"
            Condition="'$(KSPBT_GameRoot)' == ''"/>
     <ItemGroup>
       <_GameRootMessage Include="KSPBT_GameRoot Candidates:"/>

README.md

@@ -23,7 +23,7 @@ to the .csproj file. Pinning the version is highly recommended.
 
 ## Usage
 
-Once you [have a KSP installation to link to](https://kspbuildtools.readthedocs.io/en/stable/msbuild/getting-started.html#locating-your-ksp-install), all the game DLLs will be automatically included in your project automatically. 
+Once you [have a KSP installation to link to](https://kspbuildtools.readthedocs.io/en/stable/msbuild/ksp-install.html), all the game DLLs will be automatically included in your project automatically. 
 
 Configure your mod's location in GameData and where to put the output DLLs
 

docs/msbuild/index.md

@@ -21,8 +21,9 @@ maxdepth: 1
 ---
 
 getting-started
-generating-version-files
+ksp-install
 dependencies
+generating-version-files
 configuration
 ```
 

docs/msbuild/ksp-install.md

@@ -0,0 +1,25 @@
+# Locating your KSP Install
+
+KSPBuildTools needs to know where you have KSP installed in order to reference the game dlls. These are all specific to your own computer, and should not be included in your git repo.
+
+There are several options for this. KSPBuildTools will choose in the following order. Either [autodiscovery in the solution directory](#solution-directory) or [setting a reference path in a .user file](#environment-variable) are the recommended methods for most users.
+
+### KSPBT_GameRoot MSBuild Property
+
+If the {confval}`KSPBT_GameRoot` MSBuild property is already set, KSPBuildTools will use it as-is. This can be set in your .csproj.user file.
+
+### Environment Variable
+
+Set the {envvar}`KSP_ROOT` environment variable to the root of a KSP install. This is useful for CI workflows such as those using the {gha:action}`compile` action.
+
+### Solution Directory
+
+KSPBuildTools will look for a "KSP" directory in your solution directory and use it if it is a valid install. It identifies valid installs by looking for `assembly-csharp.dll` in the appropriate subdirectory for your operating system.
+
+### Reference Path
+
+KSPBuildTools will use the `ReferencePath` MSBuild property if it is a valid KSP install. This can be set in a user file located at `{csproj path}.user`. If you use Visual Studio, it can generate this file and property for you.
+
+### From Steam
+
+KSPBuildTools will use the default Steam install location if it is a valid install