added instructions to checkout deps from svn

The downloads from cmusphinx are from 2012 and don't have swig so the users should checkout from svn trunk:

```
$ ant jar
Buildfile: /Users/gina/batumihome/pocketsphinx-android/build.xml

swig:
     [exec] Unable to find file '../sphinxbase/swig/sphinxbase.i'.
     [exec] ../pocketsphinx/swig/pocketsphinx.i:65: Warning 326: Deprecated %extend name used - the struct name 'hyp_s' should be used instead of the typedef name 'Hypothesis'.
```