Update README.markdown

Co-authored-by: Datong Sun <dndx@idndx.com>

Author: chronolaw

README.markdown

@@ -7757,8 +7757,8 @@ corresponding `pkey` be provided too. See below.
 These objects can be created using [ngx.ssl.parse\_pem\_priv\_key](https://github.com/openresty/lua-resty-core/blob/master/lib/ngx/ssl.md#parse_pem_priv_key)
 function provided by lua-resty-core.
 
-If both of `cert` and `pkey` are `nil`, this method will clear
-the client certificate and private key that were setted before.
+If both of `cert` and `pkey` are `nil`, this method will clear any existing client certificate and private key
+that was previously set on the cosocket object.
 
 This method was first introduced in the `v0.10.22` release.