Fix PLIST issue (r524152) with DOCS enabled

> Checking for pkg-plist issues (check-plist)

> Parsing plist

> Checking for items in STAGEDIR missing from pkg-plist

> Checking for items in pkg-plist which are not in STAGEDIR

Error: Missing: %%DOCSDIR%%/README.txt
Error: Missing: %%DOCSDIR%%/example/client.c
Error: Missing: %%DOCSDIR%%/example/echoclient.c
Error: Missing: %%DOCSDIR%%/example/echoserver.c
Error: Missing: %%DOCSDIR%%/example/sctp-client-dtls.c
Error: Missing: %%DOCSDIR%%/example/sctp-client.c
Error: Missing: %%DOCSDIR%%/example/sctp-server-dtls.c
Error: Missing: %%DOCSDIR%%/example/sctp-server.c
Error: Missing: %%DOCSDIR%%/example/server.c
Error: Missing: %%DOCSDIR%%/example/tls_bench.c
Error: Missing: %%DOCSDIR%%/taoCert.txt

> Error: Plist issues found.

• Error code 1

Stop.
make: stopped in /usr/ports/security/wolfssl

>> Error: check-plist failures detected

Approved by: portmgr (blanket)