doc: update BUILDING.md

Added note about vcbuild being included as batch to clarify
that it's not needed from msbuild tools or visual studio.

PR-URL: https://github.com/nodejs/node/pull/8704
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

BUILDING.md

@@ -105,13 +105,13 @@ Prerequisites:
   and tools which can be included in the global `PATH`.
 
 ```console
-> vcbuild nosign
+> .\vcbuild nosign
 ```
 
 To run the tests:
 
 ```console
-> vcbuild test
+> .\vcbuild test
 ```
 
 To test if Node.js was built correctly:
@@ -169,7 +169,7 @@ $ ./configure --with-intl=full-icu --download=all
 ##### Windows:
 
 ```console
-> vcbuild full-icu download-all
+> .\vcbuild full-icu download-all
 ```
 
 #### Building without Intl support
@@ -186,7 +186,7 @@ $ ./configure --without-intl
 ##### Windows:
 
 ```console
-> vcbuild without-intl
+> .\vcbuild without-intl
 ```
 
 #### Use existing installed ICU (Unix / OS X only):
@@ -229,7 +229,7 @@ First unpack latest ICU to `deps/icu`
 as `deps/icu` (You'll have: `deps/icu/source/...`)
 
 ```console
-> vcbuild full-icu
+> .\vcbuild full-icu
 ```
 
 ## Building Node.js with FIPS-compliant OpenSSL