[minor] Incorrect value of indexdir in "Example of invocation using Java VM directly"

[kaushikacharya]

In README.md:

For MetaMapLite 3.6.1p1 (with Category 0+4+9 (USAbase) 2017AA UMLS dataset), it should be --indexdir=public_mm_lite/data/ivf/2017AA/USAbase/strict