config: documentation for HTTPS proxy client cert.

The commit adds 4 options, client cert, key, key password and CA info.
The CA info can be used to specify a different CA path to validate the
HTTPS proxy cert.

Signed-off-by: Jorge Lopez Silva <jalopezsilva@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/http.txt

@@ -29,6 +29,20 @@ http.proxyAuthMethod::
 * `ntlm` - NTLM authentication (compare the --ntlm option of `curl(1)`)
 --
 
+http.proxycert::
+	File indicating a client certificate to use to authenticate with an HTTPS proxy.
+
+http.proxykey::
+	File indicating a private key to use to authenticate with an HTTPS proxy.
+
+http.proxykeypass::
+	When communicating to the proxy using TLS (using an HTTPS proxy), use this
+	option along `http.proxykey` to indicate a password for the key.
+
+http.proxycainfo::
+	File containing the certificates to verify the proxy with when using an HTTPS
+	proxy.
+
 http.emptyAuth::
 	Attempt authentication without seeking a username or password.  This
 	can be used to attempt GSS-Negotiate authentication without specifying