Create the symlink in /usr/local/bin instead of ~/bin and make sure that /usr/local/bin in in PATH.
$ ln -s /Applications/Sublime\ Text.app/Contents/SharedSupport/bin/subl /usr/local/bin/.
$ echo $PATH
If you don’t find /usr/local/bin/, then add the following lines to your .bashrc or .zshrc:
PATH=$PATH:/usr/local/bin/; export PATH