Add note about shpc fork in README

Author: mnasiadka

roles/vault_pki/README.md

@@ -9,6 +9,10 @@ Requirements
 Note that since version `4.6.4`, `ansible-modules-hashivault` requires
 `ansible>4`.
 
+There is a fork under https://github.com/stackhpc/ansible-modules-hashivault
+that doesn't have this requirement (and is needed for the role to operate
+correctly on ansible<4).
+
 Role variables
 --------------
 
@@ -43,4 +47,4 @@ Role variables
     * `vault_pki_write_certificates_host:` The host on which certificates will be written to. (default: "localhost")
     * `vault_pki_certificates_directory`: directory to output certificate files to.
     * `vault_pki_write_certificates`: whether to write generated certificates to a file or not (default: `false`)
-    * `vault_pki_certificate_subject`: The certificate subject parameters e.g. `ttl` `ip_sans`. List of Dicts containing `{role: <name of Certificate role>, common_name: <common name of certificate>, extra_params: {ttl: <value>, alt_sans: <value>, ip_sans: <value> }}`
+    * `vault_pki_certificate_subject`: The certificate subject parameters e.g. `ttl` `ip_sans`. List of Dicts containing `{role: <name of Certificate role>, common_name: <common name of certificate>, extra_params: {ttl: <value>, alt_sans: <value>, ip_sans: <value> }}`