Ignore riscof_work and __pycache__ (riscv-non-isa#557)

Co-authored-by: Umer Shahid <[email protected]>

.gitignore

@@ -11,4 +11,7 @@
 riscv-target/
 
 #ignore venv
-riscv-isac/riscv-env
+riscv-isac/riscv-env
+
+__pycache__
+riscof_work