start-vs.cmd will point to instructions if no sln found (#4118)

Resolves #4116

docs/building.md

@@ -98,12 +98,15 @@ To find out more about the script and its parameters run: `.\build.cmd -help`.
 
 #### TL;DR
 
-Generating a new solution and opening it in Visual Studio is as easy as running:
+Generating a new "filtered" solution and opening it in Visual Studio is as easy as running:
 
 ```powershell
 > build.cmd -vs <keywords>
 ```
 
+For example, to generate a solution that contains projects with "Http" and "Fakes" in their names you can run: `.\build.cmd -vs Http,Fakes`.<br />
+If for some reason you wish to generate a solution with all projects you can pass `*` for the keyword, e.g.: `.\build.cmd -vs *`.
+
 If you already have a solution you'd like to open in Visual Studio then run the following command:
 
 ```powershell

start-code.cmd

@@ -7,7 +7,8 @@ FOR /f "delims=" %%a IN ('where.exe code') DO @SET vscode=%%a& GOTO break
 :break
 
 IF ["%vscode%"] == [""] (
-    echo [ERROR] Visual Studio Code is not installed or can't be found.
+    echo [ERROR] Visual Studio Code is not installed or can't be found.
+    echo.
     exit /b 1
 )
 
@@ -22,7 +23,8 @@ SET DOTNET_MULTILEVEL_LOOKUP=0
 SET PATH=%DOTNET_ROOT%;%PATH%
 
 IF NOT EXIST "%DOTNET_ROOT%\dotnet.exe" (
-    echo [ERROR] .NET SDK has not yet been installed. Run `%~dp0restore.cmd` to install the toolset.
+    echo [ERROR] .NET SDK has not yet been installed. Run %~dp0restore.cmd to install.
+    echo.
     exit /b 1
 )
 

start-vs.cmd

@@ -13,18 +13,25 @@ set DOTNET_MULTILEVEL_LOOKUP=0
 :: Put our local dotnet.exe on PATH first so Visual Studio knows which one to use
 set PATH=%DOTNET_ROOT%;%PATH%
 
+set SLN=SDK.sln
+if not exist "%~dp0%SLN%" (
+    echo [ERROR] %~dp0%SLN% not found.
+    echo See %~dp0%docs\building.md for instructions on how to generate a solution file.
+    echo.
+    exit /b 1
+)
+
 call restore.cmd
 
 if not exist "%DOTNET_ROOT%\dotnet.exe" (
-    echo [ERROR] .NET Core has not yet been installed. Run `%~dp0restore.cmd` to install tools
+    echo [ERROR] .NET SDK has not yet been installed. Run %~dp0restore.cmd to install.
+    echo.
     exit /b 1
 )
 
 :: Prefer the VS in the developer command prompt if we're in one, followed by whatever shows up in the current search path.
 set "DEVENV=%DevEnvDir%devenv.exe"
 
-set SLN=SDK.sln
-
 if exist "%DEVENV%" (
     :: Fully qualified works
     set "COMMAND=start "" /B "%ComSpec%" /S /C ""%DEVENV%" "%~dp0%SLN%"""