fix: rakefile and Readme file (riscv-software-src#1068)

Fixes riscv-software-src#1039

---------

Signed-off-by: Shashank V M <[email protected]>
Signed-off-by: Shashank V M <[email protected]>
Co-authored-by: Paul Clarke <[email protected]>

Author: ShashankVM

README.adoc

@@ -95,6 +95,9 @@ For convenience, running Rake inside the container is encapsulated in `do`. For
 # generate all versions of ISA manual, as an Antora static website
 ./do gen:html_manual MANUAL_NAME=isa VERSIONS=all
 
+# regenerate yaml files for the unresolved architecture
+./do gen:arch
+
 # generate an implementation-specific spec for the 'example_rv64_with_overlay' config
-./do gen:arch[example_rv64_with_overlay]
+./do gen:resolved_arch CFG=example_rv64_with_overlay
 ----

Rakefile

@@ -81,9 +81,13 @@ namespace :gen do
     end
   end
 
-  desc "Resolve the standard in arch/, and write it to gen/resolved_arch/_"
+  desc "Resolve the configuration CFG in arch/, and write it to gen/resolved_arch/<CFG>. Default CFG is the standard, \"_\"."
   task "resolved_arch" do
-    $resolver.cfg_arch_for("_")
+    cfg = ENV["CFG"]
+    if cfg.nil?
+      cfg = "_"
+    end
+    $resolver.cfg_arch_for(cfg)
   end
 end