feat first: added initial document

Signed-off-by: John Sanpe <[email protected]>

docs/manual/en_US/first.md

@@ -0,0 +1,31 @@
+# First project
+
+Let's create the first bfdev based project:
+
+```c
+#include <bfdev.h>
+
+int main(int argc, const char *argv[])
+{
+    bfdev_log_info("helloworld\n");
+    return 0;
+}
+
+```
+
+If bfdev is installed on user's local, we first need to set the environment variables, you can also add it to bashrc:
+
+```shell
+export C_INCLUDE_PATH=$C_INCLUDE_PATH:$HOME/.local/include
+export CPLUS_INCLUDE_PATH=$CPLUS_INCLUDE_PATH:$HOME/.local/include
+export LIBRARY_PATH=$LIBRARY_PATH:$HOME/.local/lib:$HOME/.local/lib64
+export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$HOME/.local/lib:$HOME/.local/lib64
+```
+
+Then we compile and run it:
+
+```
+# gcc -lbfdev -o helloworld helloworld.c
+# ./helloworld
+[info] helloworld
+```

docs/manual/index.md

@@ -7,6 +7,7 @@
 
 ## Development guide
 
+- [First project](en_US/first.md)
 - [Code layout](en_US/layout.md)
 - [Include files](en_US/include.md)