Add a Readme section for Bazelisk users

[dzintars]

Hi, all. Thank you for this plugin.
Today came across issue that Bazel binary cant be found by this plugin.
That was because i was using plain alias bazel='bazelisk' in my ~/.zshrc.
The fix of this was just a simple sudo ln -s /usr/local/bin/bazelisk /usr/local/bin/bazel. I think this could augment the readme of this plugin pretty well.

[dzintars]

Alternative is just to rename bazelisk binary to bazel, but... it's less explicit.

[dbarnett]

Yeah, symlink looks like a decent workaround, and the plugin could have an explicit way to configure the path to the bazel executable. Note I recently added 7d81632 for a similar override at command invocation time, but overriding at that level is probably not well-suited to the bazelisk case.

Would you mind suggesting some phrasing of the explanations you'd want to see in the README and/or vim help?