Update dfc document

Update certificate configuration

Change-Id: I087920d8eb0fa783ed879d3de4ed696ef1271d74
Signed-off-by: Chengkai Yan <martin.c.yan@est.tech>
Issue-ID: DCAEGEN2-876
diff --git a/docs/sections/apis/DFC.rst b/docs/sections/apis/DFC.rst
index df68064..57e2914 100644
--- a/docs/sections/apis/DFC.rst
+++ b/docs/sections/apis/DFC.rst
@@ -117,19 +117,13 @@
 
 **For TrustManager:**
 
-1. First, create a jks keystore for TrustManager:
-
- .. code:: bash
-
-   keytool -keystore ftp.jks -genkey -alias ftp
-
-2. Second, convert your certificate in a DER format :
+1. First, convert your certificate in a DER format :
 
  .. code:: bash
 
    openssl x509 -outform der -in ftp.crt -out ftp.der
 
-3. And after, import it in the keystore :
+2. And after, import it in the keystore :
 
  .. code:: bash