Add Linux and Windows installation instructions

docs/installation/windows.md

@@ -0,0 +1,25 @@
+Artifact installation instructions
+==================================
+
+We publish an archive with CoreCLR and FullCLR bits on every CI build
+with [AppVeyor][].
+
+[appveyor]: https://ci.appveyor.com/project/PowerShell/powershell-linux
+
+CoreCLR artifacts
+=================
+
+* Download zip package from **artifacts** tab of the particular build.
+* Unblock zip file: right-click in file explorer -> properties ->
+  check 'Unblock' box -> apply
+* Extract zip file to `bin` directory
+* `./bin/powershell.exe`
+
+FullCLR artifacts
+=================
+
+* Download zip package from **artifacts** tab of the particular build.
+* Unblock zip file: right-click in file explorer -> properties ->
+  check 'Unblock' box -> apply
+* Extract zip file to `$in` directory
+* `Start-DevPSGithub -binDir bin`