Update build to reflect PRODUCTION_BUILD option

Update documentation.

Makefile

@@ -133,6 +133,10 @@ ifeq ($(DEBUG),1)
 DEFINES += ZEMU_LOGGING
 endif
 
+ifeq ($(PRODUCTION_BUILD),1)
+DEFINES += PRODUCTION_BUILD=1
+endif
+
 #########################
 
 # Import generic rules from the SDK

README.md

@@ -51,6 +51,7 @@ make
 make BOLOS_SDK=$NANOX_SDK
 make BOLOS_SDK=$NANOSP_SDK
 make BOLOS_SDK=$STAX_SDK
+make BOLOS_SDK=$FLEX_SDK
 ```
 
 Stax app can be compiled in DEBUG mode for debugging purposes
@@ -59,6 +60,12 @@ make BOLOS_SDK=$STAX_SDK DEBUG=1
 ```
 Note, that it is possible (although unlikely) for ledger to make a braking change in ledger-app-dev-tools:latest. 
 
+Note, that the build by default builds a build with captions showing that it is a demo app. To replace the captions with correct ones one should use e.g.
+
+```shell
+make BOLOS_SDK=$STAX_SDK PRODUCTION_BUILD=1
+```
+
 #### Tests
 
 ##### Speculos integration tests
@@ -71,6 +78,7 @@ pytest tests/ --tb=short -v --device nanos
 pytest tests/ --tb=short -v --device nanox
 pytest tests/ --tb=short -v --device nanosp
 pytest tests/ --tb=short -v --device stax
+pytest tests/ --tb=short -v --device flex
 ```
 
 Note that in case ledger-app-dev-tools:latest is updated there is a chance that slight changes in gui happen. In that case it is necessary to re-generate the snapshots, e.g.
@@ -99,6 +107,7 @@ make scan-build
 make scan-build BOLOS_SDK=$NANOX_SDK
 make scan-build BOLOS_SDK=$NANOSP_SDK
 make scan-build BOLOS_SDK=$STAX_SDK
+make scan-build BOLOS_SDK=$FLEX_SDK
 ```
 
 ## Further information