short documentation on how to request a cert from a Windows CA

doc/Windows-Certificate.asciidoc

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+Request and load a certificate from Windows CA
+----------------------------------------------
+
+This is a short step-by-step on how to generate a key in the Neo,
+create a certificate request, submit that request to a Windows CA
+and then load the certificate in the Neo.
+
+Prerequisites
+-------------
+
+* a YubiKey Neo with the PIV applet loaded
+* the yubico-piv-tool software
+* credentials to request certs from a Windows CA
+
+Steps
+-----
+
+1. Generate the key:
+
+  yubico-piv-tool -s 9a -a generate -o public.pem
+
+2. Request a certificate:
+
+  yubico-piv-tool -a verify-pin -P 123456 -s 9a -a request-certificate -S "/CN=example/O=test/" \
+		-i public.pem -o request.csr
+
+3. Submit the request to the Windows CA:
+   (this step must be run on a windows machine that know about the CA)
+
+  certreq -submit -attrib "CertificateTemplate:User" request.csr cert.crt
+
+4. Load the certificate in the Neo:
+
+  yubico-piv-tool -s 9a -a import-certificate -i cert.crt
+
+5. For it to be useful in windows a chuid must be set as well:
+   (only if that wasn't done earlier)
+
+	 yubico-piv-tool -a set-chuid