[stm32variant] Add a README.md

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

CI/utils/README.md

@@ -0,0 +1,34 @@
+# stm32variant
+
+By default, generates:
+ - *PeripheralPins.c*
+ - *PinNamesVar.h*
+ - *variant_generic.cpp*
+ - *variant_generic.h*
+ - *boards_entry.txt*
+ - *generic_clock.c*
+
+for all xml files description available in [STM32CubeMX](http://www.st.com/en/development-tools/stm32cubemx.html) internal database.
+Internal database path have to be defined in `variant_config.json`.
+It can be the one from STM32CubeMX directory if defined or the one from GitHub:
+
+https://github.com/STMicroelectronics/STM32_open_pin_data
+
+After file generation, review them carefully and please report any issue
+[here](https://github.com/stm32duino/Arduino_Core_STM32/issues).
+
+
+### Usage:
+
+  `python genpinmap_arduino.py [-h] [-l | -m xml]`
+
+
+### Optional arguments:
+
+  `-h`, `--help` &emsp;&emsp;&emsp;&emsp;&emsp;&emsp; Show this help message and exit<br>
+  `-l`, `--list` &emsp;&emsp;&emsp;&emsp;&emsp;&emsp; List available xml files description in database<br>
+  `-f name`, `--family name`&nbsp;                    Generate all files for specified mcu family.<br>
+  `-c`, `--cube` &emsp;&emsp;&emsp;&emsp;&emsp;&emsp; Use STM32CubeMX internal database. Default use GitHub STM32_open_pin_data repository.<br>
+  `-s`, `--skip` &emsp;&emsp;&emsp;&emsp;&emsp;&emsp; Skip STM32_open_pin_data clone/fetch<br>
+
+All generated files are available under _./variants/<mcu_serie>/<mcu_names>_ directory