update readme.md

Author: ajz34

dftd3/src/damping_param_usage.md

@@ -4,7 +4,7 @@ If your task is to retrive damping parameters of some specific xc-functionals, y
 
 In this crate, you may have three ways to define customized parameters:
 
-- By `DFTD3***DampingParam` struct. In this way, all parameters (include optional parameters with default value) must be provided. For example of B3-Zero:
+- By `DFTD3***DampingParam` struct. In this way, all parameters (include optional parameters with default value) must be provided. For example of D3-Zero:
 
     ```rust
   # use dftd3::prelude::*;
@@ -21,7 +21,7 @@ In this crate, you may have three ways to define customized parameters:
     // this will give param: DFTD3Param
     ```
 
-- By `DFTD3***DampingParamBuilder` struct. In this way, optional parameters can be omitted. For example of B3-Zero:
+- By `DFTD3***DampingParamBuilder` struct. In this way, optional parameters can be omitted. For example of D3-Zero:
 
     ```rust
   # use dftd3::prelude::*;
@@ -34,7 +34,7 @@ In this crate, you may have three ways to define customized parameters:
     // this will give param: DFTD3Param
     ```
 
-- By `DFTD3Param` utility. In this way, all parameters must be provided. For example of B3-Zero:
+- By `DFTD3Param` utility. In this way, all parameters must be provided. For example of D3-Zero:
 
     ```rust
   # use dftd3::prelude::*;

readme.md

@@ -123,6 +123,11 @@ If you have not compiled `s-dftd3` library, you may try out cargo feature `build
 ### Cargo features of `dftd3-src`
 
 - **`build_from_source`**: This will use CMake and meson, and pull code from github to first perform build for simple-dftd3. Though this option can be developer-friendly (you do not need to perform any other configurations to make program compile and run by cargo), `build_from_source` does not provide customized compilation.
+
+    CMake configurable variables (can be defined as environment variables):
+    - `DFTD3_SRC`: git repository source directory or URL;
+    - `DFTD3_VER`: version of DFT-D4 (default v1.2.1);
+
 - **`static`**: This will link static libary instead of dynamic one. Please note that 1. static linking may require additional Fortran and OpenMP linking, which is not provided in this crate; 2. staticly linking LGPL-3.0 license may require your project to be GPL-3.0.
 
 ## License