Use README for gen:html_manual task description

Author: dhower-qc

README.adoc

@@ -10,7 +10,7 @@ data become validated, we will list it here.
 
 == Quick links
 
-* https://riscv-software-src.github.io/riscv-unified-db/index.html[The **UNOFFICIAL** latest UDB-generated RISC-V specifications].
+* https://riscv-software-src.github.io/riscv-unified-db/index.html[The latest UDB-generated **UNOFFICIAL** RISC-V specifications].
 * UDB Documentation
 ** xref:doc/schemas.adoc[Schema documentation]
 ** xref:doc/idl.adoc[ISA Description Language (IDL)]

backends/manual/README.adoc

@@ -0,0 +1,17 @@
+Generate an HTML site for one or more versions of the manual (./do --desc for options)
+
+== Usage
+
+Options:
+
+  * MANUAL_NAME: The database name (key) of the manual to generate.
+  * VERSIONS: A comma-separated list of versions to generate, or "all".
+
+Examples:
+
+  ./do gen:html_manual MANUAL_NAME=isa VERSIONS=20191008,20240411
+  ./do gen:html_manual MANUAL_NAME=isa VERSIONS=all
+
+Result:
+
+  A static HTML website will be written into gen/manual/MANUAL_NAME/<hash of versions>/html

backends/manual/tasks.rake

@@ -377,24 +377,7 @@ rule %r{#{MANUAL_GEN_DIR}/[^/]+/[^/]+/riscv-isa-manual/README.md} => ["#{$root}/
 end
 
 namespace :gen do
-  html_manual_desc = <<~DESC
-    Generate an HTML site for one or more versions of the manual (./do --desc for options)
-
-    Options:
-
-     * MANUAL_NAME: The database name (key) of the manual to generate.
-     * VERSIONS: A comma-separated list of versions to generate, or "all".
-
-    Examples:
-
-     ./do gen:html_manual MANUAL_NAME=isa VERSIONS=20191008,20240411
-     ./do gen:html_manual MANUAL_NAME=isa VERSIONS=all
-
-    Result:
-
-      A static HTML website will be written into gen/manual/MANUAL_NAME/<hash of versions>/html
-  DESC
-  desc html_manual_desc
+  desc File.read("#{File.dirname(__FILE__)}/README.adoc")
   task :html_manual do
     raise ArgumentError, "Missing required environment variable MANUAL_NAME\n\n#{html_manual_desc}" if ENV["MANUAL_NAME"].nil?
     raise ArgumentError, "Missing required environment variable VERSIONS\n\n#{html_manual_desc}" if ENV["VERSIONS"].nil?