Clarify dependencies

doc/src/installation.md

@@ -1,5 +1,20 @@
 # Installation
 
+## Dependencies
+
+End users (and distributions) are encouraged to use the tarball, which only
+depends on Python and a few Python packages (`llvmlite`, `pytest`,
+`prompt_toolkit` and `antlr4-python3-runtime`). The LFortran standard library
+needs to be compiled and it needs a C compiler. Down the road (see our
+[roadmap](index.md)), LFortran will be gradually rewritten in C++, so it will
+also depend on a C++ compiler.
+
+The tarball is generated automatically by our CI (continuous integration) and
+contains some autogenerated files: the parser, which is generated by ANTLR4
+(requires Java) and the AST and ASR nodes, which is generated by an ASDL
+translator (requires Python). The Java requirement is only needed when using
+git directly, the tarball does not depend on Java in any way.
+
 ## From a Tarball
 
 This is the easiest way.