[doc] Increment the documentation

Signed-off-by: Douglas Reis <doreis@lowrisc.org>

Author: engdoreis

README.md

@@ -1,2 +1,80 @@
 # reisfmt
-A tiny implementation of the c++23 std::print for embedded systems.
+This is a tiny implementation, header only of the c++23 std::print for embedded systems.
+It only depend on some headers of the standard lib.
+
+## How to download using CMake
+```Cmake
+<!-- CMakelist.txt -->
+cmake_minimum_required(VERSION 3.13)
+include(FetchContent)
+
+FetchContent_Declare(REISFMT
+  GIT_REPOSITORY    https://github.com/engdoreis/reisfmt
+  GIT_TAG           <git hash>
+)
+FetchContent_Populate(REISFMT)
+
+set(NAME my_app)
+add_executable(${NAME} main.cc)
+target_include_directories(${NAME} PRIVATE "${reisfmt_SOURCE_DIR}/include")
+```
+
+## How to instantiate in your project
+```cpp
+// log.hh
+#include "fmt.h"
+#include "uart.h"
+
+struct LogUart{
+  Uart* uart;
+  // Implement your serialization here (UART, USB...)
+  void write(const char* buf, size_t n) {
+    while (n--) {
+      uart->putc(*buf++);
+    }
+  }
+};
+
+using Log = reisfmt::Fmt<LogUart>;
+
+//main.cc
+#include "log.h"
+//...
+int main() {
+// ...
+  LogUart log_uart{uart0};
+  Log log(log_uart);
+  log.print("Hello {}", "World");
+  return 0;
+}
+```
+
+## Formating specification
+This library follows the libc++ format specification defined [here](https://en.cppreference.com/w/cpp/utility/format/spec).
+
+The following features above from the specifications are implemented:
+
+|Spec|Implmented|
+|-|-|
+|fill-and-align|yes|
+|sign|no|
+|#|yes|
+|width|yes|
+|precision|no|
+|locale|no|
+|type| See below|
+
+|Type|Implmemented|
+|-|-|
+|d|yes|
+|b|yes|
+|x|yes|
+|o|yes|
+|f|no|
+|a|no|
+|e|no|
+|g|no|
+|p|no|
+|?|no|
+
+