update FlowVariables.md

Signed-off-by: Eder Monteiro <[email protected]>

Author: eder-matheus

docs/user/FlowVariables.md

@@ -157,6 +157,7 @@ configuration file.
 | <a name="IO_PLACER_H"></a>IO_PLACER_H| A list of metal layers on which the I/O pins are placed horizontally (top and bottom of the die).| |
 | <a name="IO_PLACER_V"></a>IO_PLACER_V| A list of metal layers on which the I/O pins are placed vertically (sides of the die).| |
 | <a name="IR_DROP_LAYER"></a>IR_DROP_LAYER| Default metal layer to report IR drop.| |
+| <a name="KEEP_VARS"></a>KEEP_VARS| Feature toggle to keep intermediate variables during the flow. This is useful for the single-run flow, where all stages of the flow are run in a single OpenROAD instance.| |
 | <a name="KLAYOUT_TECH_FILE"></a>KLAYOUT_TECH_FILE| A mapping from LEF/DEF to GDS using the KLayout tool.| |
 | <a name="LATCH_MAP_FILE"></a>LATCH_MAP_FILE| Optional mapping file supplied to Yosys to map latches| |
 | <a name="LAYER_PARASITICS_FILE"></a>LAYER_PARASITICS_FILE| Path to per layer parasitics file. Defaults to $(PLATFORM_DIR)/setRC.tcl.| |
@@ -482,6 +483,7 @@ configuration file.
 
 ## All stages variables
 
+- [KEEP_VARS](#KEEP_VARS)
 - [NUM_CORES](#NUM_CORES)
 - [OPENROAD_HIERARCHICAL](#OPENROAD_HIERARCHICAL)
 - [SWAP_ARITH_OPERATORS](#SWAP_ARITH_OPERATORS)