DOCSP-15632 add C driver to CSFLE compatibility table

Author: andf-mongodb

source/core/security-client-side-encryption.txt

@@ -440,6 +440,10 @@ the following official 4.2+ compatible driver versions:
      - ``2.10.0+``
      - `.NET Driver Quickstart <https://mongodb.github.io/mongo-csharp-driver/2.10/reference/driver/crud/client_side_encryption/>`__
 
+   * - :ecosystem:`C </drivers/c/>`
+     - ``1.17.5``
+     - `C Driver Client-Side Field Level Encryption <http://mongoc.org/libmongoc/current/using_client_side_encryption.html>`__
+
    * - :ecosystem:`Go </drivers/go/>` 
      - ``1.2+``
      - `Go Driver Quickstart <https://godoc.org/go.mongodb.org/mongo-driver/mongo#hdr-Client_Side_Encryption>`__