Small updates on documents:

- README.md
- CONTRIBUTING.md
- doc/limitations.md

CONTRIBUTING.md

@@ -56,7 +56,7 @@ on-demand.
 
 Use C++ style comments only for temporary comment e.g. commenting out some code lines.
 
-#### Insert a break after the method return value:
+#### Insert a break after the function return value:
 
     int
     main(void)
@@ -72,4 +72,5 @@ language itself. Please note the following hints for your Ruby code:
 #### Comply with the Ruby standard (ISO/IEC 30170:2012)
 
 mruby is currently targeting to execute Ruby code which complies to ISO/IEC
-30170:2012 (http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=59579).
+30170:2012 (http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=59579),
+unless there's a clear reason, e.g. the latest Ruby has changed behavior from ISO.

README.md

@@ -40,11 +40,13 @@ We don't have a mailing list, but you can use [GitHub issues](https://github.com
 
 See the [compile.md](https://github.com/mruby/mruby/blob/master/doc/guides/compile.md) file.
 
-## Running Tests
+## How to Build
 
-To run the tests, execute the following from the project's root directory.
+To build mruby, execute the following from the project's root directory.
 
-    $ rake test
+  $ rake TARGET=<target> test
+
+The default `TARGET` is `host`. `TARGET` will be loaded from `target` directory.
 
 Note: `bison` bundled with MacOS is too old to compile `mruby`.
 Try `brew install bison` and follow the instuction shown to update

doc/limitations.md

@@ -245,8 +245,7 @@ trace (most recent call last):
 ## Keyword arguments
 
 mruby keyword arguments behave slightly different from CRuby 2.5
-to make the behavior simpler and less confusing. Maybe in the
-future, the simpler behavior will be adopted to CRuby as well.
+to make the behavior simpler and less confusing. 
 
 #### Ruby [ruby 2.5.1p57 (2018-03-29 revision 63029)]
 
@@ -264,6 +263,20 @@ trace (most recent call last):
 -e:1: keyword argument hash with non symbol keys (ArgumentError)
 ```
 
+## `nil?` redefinition in conditional expressions
+
+Redefinition of `nil?` is ignored in conditional expressions.
+
+```ruby
+a = "a"
+def a.nil?
+  true
+end
+puts(a.nil? ? "truthy" : "falsy")
+```
+
+Ruby outputs `falsy`. mruby outputs `truthy`.
+
 ## Argument Destructuring
 
 ```ruby
@@ -283,17 +296,3 @@ f(1,[2,3])
 ```
 
 CRuby gives `[1,2,3,nil]`. mruby raises `NoMethodError` for `b`.
-
-## `nil?` redefinition in conditional expressions
-
-Redefinition of `nil?` is ignored in conditional expressions.
-
-```ruby
-a = "a"
-def a.nil?
-  true
-end
-puts(a.nil? ? "truthy" : "falsy")
-```
-
-Ruby outputs `falsy`. mruby outputs `truthy`.