Documentation update per conversion/database tool changes

docs/usage/tools.md

@@ -6,9 +6,7 @@ ECNet databases are comma-separated value (CSV) formatted files that provide inf
 
 Our [databases](https://github.com/ECRL/ECNet/tree/master/databases) directory on GitHub contains databases for cetane number, cloud point, kinetic viscosity, pour point and yield sooting index, as well as a database template.
 
-You can create an ECNet-formatted database with molecule names or SMILES and (optionally) target values. The following programs must be installed for you to do so:
-- [Open Babel](http://openbabel.org/wiki/Main_Page) software
-- [Java JRE](https://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html) version 6 and above
+You can create an ECNet-formatted database with molecule names or SMILES and (optionally) target values. [Java JRE](https://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html) version 6 and above is required to create a database.
 
 Supplied names or SMILES must exist in a text file, one entry per line:
 ```
@@ -70,6 +68,8 @@ smiles = get_smiles('Molecule Name')
 
 ### SMILES string to MDL Molfile
 
+Creating an MDL file requires [Open Babel](http://openbabel.org/wiki/Main_Page) to be installed.
+
 A text file containing SMILES strings, one per line, is required:
 
 ```
@@ -100,6 +100,19 @@ from ecnet.tools.conversions import mdl_to_descriptors
 mdl_to_descriptors('molfile.md', 'descriptors.csv')
 ```
 
+### SMILES string to QSPR descriptors
+
+A text file containing SMILES strings, one per line, is required, as well as an installation of [Java JRE](https://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html).
+
+*Note: the file extension for the text file containing SMILES strings must be ".smi"
+
+```python
+from ecnet.tools.conversions import smiles_to_descriptors
+
+# A CSV file with descriptors is generated
+smiles_to_descriptors('molecules.smi', 'descriptors.csv')
+```
+
 ## ECNet .prj file usage
 
 Once an ECNet project has been created, the resulting .prj file can be used to predict properties for new molecules. A text file containing names or SMILES strings of new molecules, one per line, is required in addition to the .prj file.