Add instructions on how to use github with a subversion client.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3396 44740490-163a-0410-bde0-09ae8108e29a

docs/simplesamlphp-install-repo.txt

@@ -50,4 +50,9 @@ If you installed SimpleSAMLphp from subversion, and want to keep updated on the
 your installation to git. First, follow the steps to get a fresh install from github in a different directory. Skip the
 steps regarding configuration and metadata initialization, and copy all the files you might have modified instead (not
 only configuration and metadata, but also any custom modules or templates). Finally, proceed to install Composer and
-install all the dependencies with it. You may want to add all your custom files to the '.gitignore' file.
\ No newline at end of file
+install all the dependencies with it. You may want to add all your custom files to the '.gitignore' file.
+
+If you really want to use subversion instead of git, or it is impossible for you to migrate (you cannot install git, for
+example), you might want to do a fresh install like the one described here, but using github's subversion interface.
+Refer to [github's documentation](https://help.github.com/articles/support-for-subversion-clients) for detailed
+instructions on how to do that.