DOC: readme: add suggestion to link against static openssl

Adds a suggestion in README howto link against a static build of openssl.

This is useful if the OS includes an old openssl releas and recent features
or ciphers are required.
diff --git a/README b/README
index 54ba1b7..9c0bca3 100644
--- a/README
+++ b/README
@@ -90,6 +90,17 @@
 if the build fails due to missing symbols such as deflateInit(), then try again
 with "ADDLIB=-lz".
+To link OpenSSL statically against haproxy, build OpenSSL with the no-shared
+keyword and install it to a local directory, so your system is not affected :
+    $ export STATICLIBSSL=/tmp/staticlibssl
+    $ ./config --prefix=$STATICLIBSSL no-shared
+    $ make && make install_sw
+When building haproxy, pass that path via ADDINC and ADDLIB to make and include
+libdl ("-ldl").
 It is also possible to include native support for ZLIB to benefit from HTTP
 compression. For this, pass "USE_ZLIB=1" on the "make" command line and ensure
 that zlib is present on the system.