Add instructions for building from Git repo in README file

[jjts]

after download and following the instructions in the README file

./configure
bash: ./configure: No such file or directory

[jjts]

just tell the user to run
./autogen.sh

[njh]

For end-users, I recommend installing from tar.gz, not from the git repo:
http://www.twolame.org

Although I acknowledge that it has been a long time since I did a new release.

Part of the steps of building the tar.gz creates the configure script.
Perhaps there should be a DEVELOP.md file giving instructions for working on the twolame codebase.

[vtorri]

btw, to create the tarball, if autotools are correctly done, just do :

make distcheck

it creates the tarball uncompress it, compile the source, install in a subdir, launch the tests, uninstall (and check there is no left files), remove subdir.

so you are sure that the tarball compiles and tests are successful