improve README

README.md

@@ -1,12 +1,46 @@
 # rv
 
-TODOs:
-
-- [ ] Support more instructions
-- [ ] CSR
-- [x] Load ELF
-- [ ] Memory mapped IO devices
-- [ ] Exception
-- [ ] Interrupt
-- [ ] CPU mode
-- [ ] Virtual memory translation
+rv is a 64-bit RISC-V emulator written in Go.
+It only supports running ELF binary.
+
+## Installation
+
+```
+go install github.com/hidetatz/rv@latest
+```
+
+## Usage
+
+Pass an ELF program to run to `rv`.
+
+```
+rv -p ./hello
+```
+
+Debug will be enabled if `-d` option is passed.
+
+## Supported instructions
+
+- [ ] RV64G ISA
+  - [x] RV64I
+  - [ ] RV64M
+  - [ ] RV64A
+  - [ ] RV64F
+  - [ ] RV64D
+  - [x] Zifencei
+  - [x] Zicsr
+- [x] RV64C ISA
+- [x] Privileged ISA
+
+For the full list of the implemented instructions, see [instructions.go](./instructions.go).
+
+## Supported features
+
+- [x] ELF binary load
+- [ ] Sv39 (Virtual memory)
+- [x] CSR
+- [ ] Devices
+
+## LICENSE
+
+MIT