Update build instructions.

README.md

@@ -22,7 +22,7 @@ Try it
Clone the repo, build the Python extension, and run `bin/osh`.  Basic things
like pipelines, variables, functions, etc. should work.

    bash$ build/dev.sh all
    bash$ build/dev.sh minimal
    ...
    # Now you should have a libc.so symlink in the repository root directory

@@ -31,8 +31,8 @@ like pipelines, variables, functions, etc. should work.
    osh$ echo "hello $name"
    hello world

You can also try the [Oil 0.0
release](https://www.oilshell.org/blog/2017/07/23.html).
You can also download the latest release and build it, which is linked from the
[home page](https://www.oilshell.org/).

Contributing
------------