README.org: Add a note about ssl certificates

Dockerfile

@@ -4,6 +4,8 @@ ADD links.tar.gz /
 ADD passwd /etc/passwd
 ADD passwd /tmp/proot/delete-me
 
+ENV SSL_CERT_DIR=/etc/ssl/certs
+ENV SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
 ENV GUIX_LOCPATH=/guix-builder/lib/locale
 ENV PROOT_TMP_DIR=/tmp/proot
 RUN rm /tmp/proot/delete-me

README.org

@@ -61,6 +61,9 @@ Depending on use-case, it is sometimes useful to retain the guix cache between c
 invocations. To do so, mount a volume to ~$HOME/.cache/guix~ (replacing ~$HOME~ with what it
 will be set to within the container).
 
+SSL certificates are included and configured for use in the container (via the ~nss-certs~
+package). However, it is recommended to use your hosts certificate files via a volume mount.
+
 A complete example is given below, where the aforementioned volumes are mounted, ~HOME~ is
 set to ~/tmp~, and a volume for retaining the guix cache between invocations is put in place.
 The working directory within the container is also set with the ~-w~ option, however this is