Move rsconscache into build directory - close #136

doc/user_guide.md

@@ -78,9 +78,12 @@ cache file in order to avoid rebuilding a target when it is already up to date.
 ### Build Directory
 
 Rscons was designed to store temporary build artifacts (for example, object
-files, dependency files, etc...) in a `build` directory.
+files, dependency files, etc...) and build system metadata in a
+"build directory".
 This keeps files generated by the build cleanly separated from user-controlled
 source files.
+By default a build directory named "build" is used, but this can be overridden
+by the user by using the `-b`/`--build` command-line option.
 
 ## Getting Started
 
@@ -94,7 +97,7 @@ To use Rscons on your project, you must:
 
 Rscons is designed to be distributed as a stand-alone single file script that
 can be copied into and versioned in a project's source tree.
-The only dependency required to run Rscons is to have a Ruby interpreter
+The only requirement to run Rscons is that the system has a Ruby interpreter
 installed.
 The latest release can be downloaded from [https://github.com/holtrop/rscons/releases](https://github.com/holtrop/rscons/releases).
 Simply copy the `rscons` executable script into the desired location within