add more links to README

README.md

@@ -4,10 +4,6 @@ Decaf is a Java-like, but much smaller programming language mainly for education
 We now have at least three different implementations of the compiler in Java, Scala and Rust.
 Since the standard language has quite a limited set of language features, students are welcome to add their own new features.
 
-We are happy to announce that this new compiler, written in Java, is now tested upon a partial set of Decaf programs, from parsing to emitting MIPS assembly code. However, a lot of work will be done in a couple of weeks -- refactoring, documenting and revising to meet the new Decaf language standard. More materials are coming soon.
-
-The final version for the compiler course will be ready right before the publication of the first PA assignment.
-
 ## Getting Started
 
 This project requires JDK 12.
@@ -39,10 +35,29 @@ to display the usage help.
 Possible targets/tasks are:
 
 - PA1: parse source code and output the pretty printed tree, or error messages
+- PA1-LL: like PA1, but use hand-coded LL parsing algorithm, with the help of a LL table generator [ll1pg](https://github.com/paulzfm/ll1pg)
 - PA2: type check and output the pretty printed scopes, or error messages
 - PA3: generate TAC (three-address code), dump it to a .tac file, and then output the execution result using our built-in simulator
 - PA4: currently same with PA3, will be reserved for students to do a bunch of optimizations on TAC
 - PA5: (default target) allocate registers and emit assembly code, currently we are using a very brute-force algorithm and only generates MIPS assembly code (with pseudo-ops, and no delayed branches)
 
 To run the MIPS assembly code, you may need [spim](http://spimsimulator.sourceforge.net), a MIPS32 simulator.
 For Mac OS users, simply install `spim` with `brew install spim` and run with `spim -file your_file.s`.
+
+## Releases
+
+See https://github.com/decaf-lang/decaf/releases for releases, including separate frameworks for PA1 -- PA3.
+
+## Materials
+
+We have a couple of Chinese documents on the language specification and implementation outlines:
+
+- https://decaf-lang.gitbook.io
+- https://decaf-project.gitbook.io
+
+## Development & Contribution
+
+In future, we will develop on (possibly variates of) development branches,
+and only merge release versions into the master branch.
+
+Issues and pull requests for fixing bugs are welcome. However, adding new language features will not be considered, because that's students' work!