Add CA bundle reference in the docs

Author: sohankunkerkar

doc/configuration-v3_0.md

@@ -19,7 +19,7 @@ The Ignition configuration is a JSON document conforming to the following specif
   * **_security_** (object): options relating to network security.
     * **_tls_** (object): options relating to TLS when fetching resources over `https`.
       * **_certificateAuthorities_** (list of objects): the list of additional certificate authorities (in addition to the system authorities) to be used for TLS verification when fetching over `https`. All certificate authorities must have a unique `source`.
-        * **source** (string): the URL of the certificate (in PEM format). Supported schemes are `http`, `https`, `s3`, `tftp`, and [`data`][rfc2397]. Note: When using `http`, it is advisable to use the verification option to ensure the contents haven't been modified.
+        * **source** (string): the URL of the certificate bundle (in PEM format). The bundle can contain multiple concatenated certificates. Supported schemes are `http`, `https`, `s3`, `tftp`, and [`data`][rfc2397]. Note: When using `http`, it is advisable to use the verification option to ensure the contents haven't been modified.
         * **_verification_** (object): options related to the verification of the certificate.
           * **_hash_** (string): the hash of the certificate, in the form `<type>-<value>` where type is sha512.
 * **_storage_** (object): describes the desired state of the system's storage devices.

doc/configuration-v3_1.md

@@ -27,7 +27,7 @@ The Ignition configuration is a JSON document conforming to the following specif
   * **_security_** (object): options relating to network security.
     * **_tls_** (object): options relating to TLS when fetching resources over `https`.
       * **_certificateAuthorities_** (list of objects): the list of additional certificate authorities (in addition to the system authorities) to be used for TLS verification when fetching over `https`. All certificate authorities must have a unique `source`.
-        * **source** (string): the URL of the certificate (in PEM format). Supported schemes are `http`, `https`, `s3`, `tftp`, and [`data`][rfc2397]. Note: When using `http`, it is advisable to use the verification option to ensure the contents haven't been modified.
+        * **source** (string): the URL of the certificate bundle (in PEM format). The bundle can contain multiple concatenated certificates. Supported schemes are `http`, `https`, `s3`, `tftp`, and [`data`][rfc2397]. Note: When using `http`, it is advisable to use the verification option to ensure the contents haven't been modified.
         * **_compression_** (string): the type of compression used on the certificate (null or gzip). Compression cannot be used with S3.
         * **_httpHeaders_** (list of objects): a list of HTTP headers to be added to the request. Available for `http` and `https` source schemes only.
           * **name** (string): the header name.

doc/configuration-v3_2_experimental.md

@@ -29,7 +29,7 @@ The Ignition configuration is a JSON document conforming to the following specif
   * **_security_** (object): options relating to network security.
     * **_tls_** (object): options relating to TLS when fetching resources over `https`.
       * **_certificateAuthorities_** (list of objects): the list of additional certificate authorities (in addition to the system authorities) to be used for TLS verification when fetching over `https`. All certificate authorities must have a unique `source`.
-        * **source** (string): the URL of the certificate (in PEM format). Supported schemes are `http`, `https`, `s3`, `tftp`, and [`data`][rfc2397]. Note: When using `http`, it is advisable to use the verification option to ensure the contents haven't been modified.
+        * **source** (string): the URL of the certificate bundle (in PEM format). The bundle can contain multiple concatenated certificates. Supported schemes are `http`, `https`, `s3`, `tftp`, and [`data`][rfc2397]. Note: When using `http`, it is advisable to use the verification option to ensure the contents haven't been modified.
         * **_compression_** (string): the type of compression used on the certificate (null or gzip). Compression cannot be used with S3.
         * **_httpHeaders_** (list of objects): a list of HTTP headers to be added to the request. Available for `http` and `https` source schemes only.
           * **name** (string): the header name.