added notes about optional lxml install

Author: fracpete

README.md

@@ -10,7 +10,8 @@ Requirements:
   * matplotlib (optional)
   * pygraphviz (optional)
   * PIL (optional)
-* JDK 8 or later (OpenJDK 11 recommended)
+  * lxml (optional)
+* OpenJDK 11 (or later)
 
 Uses:
 * Weka (3.9.6)

doc/source/index.rst

@@ -36,8 +36,9 @@ The library has the following requirements:
  * pygraphviz (optional)
  * PIL (optional)
  * matplotlib (optional)
+ * lxml (optional)
 
-* Oracle JDK 1.8 or later (JDK 11 recommended)
+* OpenJDK 11 (or later)
 
 Uses:
 

doc/source/install.rst

@@ -227,6 +227,7 @@ You need to install the following Python packages:
 * pillow
 * matplotlib
 * pygraphviz
+* lxml
 * python-javabridge
 
 Once these libraries are installed, you can use ``pip`` to install the remaining