README warns about Windows path lengths (#168)

Author: graebm

README.md

@@ -54,6 +54,9 @@ cmake -DCMAKE_INSTALL_PREFIX="<absolute path sdk-cpp-workspace dir>"  -DCMAKE_PR
 cmake --build . --target install
 ```
 
+#### Building on Windows
+Due to maximum path length limitations in the Windows API, we recommend [enabling long paths](https://docs.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation#enable-long-paths-in-windows-10-version-1607-and-later) on your development machines, or cloning to a short path like: `C:\dev\iotsdk`
+
 ### Mac-Only TLS Behavior
 
 Please note that on Mac, once a private key is used with a certificate, that certificate-key pair is imported into the Mac Keychain.  All subsequent uses of that certificate will use the stored private key and ignore anything passed in programmatically.  Beginning in v1.7.3, when a stored private key from the Keychain is used, the following will be logged at the "info" log level: