javadoc: add page (#3567)

pages/common/javadoc.md

@@ -0,0 +1,16 @@
+# javadoc
+
+> Generate Java API documentation in HTML format from source code.
+> More information: <https://docs.oracle.com/javase/9/javadoc/javadoc-command.htm>.
+
+- Generate documentation for Java source code and save the result in a directory:
+
+`javadoc -d {{path/to/directory/}} {{path/to/java_source_code}}`
+
+- Generate documentation with a specific encoding:
+
+`javadoc -docencoding {{UTF-8}} {{path/to/java_source_code}}`
+
+- Generate documentation excluding some packages:
+
+`javadoc -exclude {{package_list}} {{path/to/java_source_code}}`