Update README.md (#41)

Signed-off-by: Victor Smirnov <[email protected]>

Author: vityaman

README.md

@@ -8,6 +8,12 @@ Repository for the ITMO CSE OS course.
 
 - [БЛР2: Page Cache](./lab/vtpc/README.md)
 
-- [ПЛР: Файловая система](./lab/vtfs/README.md)
+- [ПЛР1: Введение в Xv6](https://github.com/secs-dev/xv6-riscv/blob/main/doc/lab/1.md)
+
+- [ПЛР2: Аллокатор](https://github.com/secs-dev/xv6-riscv/blob/main/doc/lab/2.md)
+
+- [ПЛР3: Copy-on-write fork](https://github.com/secs-dev/xv6-riscv/blob/main/doc/lab/3.md)
+
+- [ПЛР4: Файловая система](./lab/vtfs/README.md)
 
 - [Порядок сдачи ЛР](./doc/process.md)