Adds variable (rakudo-specific). Refs #2547

doc/Language/variables.pod6

@@ -1114,17 +1114,16 @@ C<$!> is the error variable. If a C<try> block or statement prefix catches
 an exception, that exception is stored in C<$!>. If no exception was caught,
 C<$!> is set to the C<Any> type object.
 
-Note that C<CATCH> blocks I<do not> set C<$!>. Rather they set C<$_> inside
+Note that C<CATCH> blocks I<do not> set C<$!>. Rather, they set C<$_> inside
 the block to the caught exception.
 
 X<|$?FILE>X<|$?LINE>X<|::?CLASS>X<|&?BLOCK>X<|%?RESOURCES>
 =head2 Compile-time variables
 
-All compile time variables have a question mark as part of the twigil.
-Being I<compile time> they cannot
-be changed at runtime, however they are valuable in order to introspect
-the program.
-The most common compile time variables are the following:
+All compile time variables have a question mark as part of the twigil. Being
+I<compile time> they cannot be changed at runtime, however they are valuable in
+order to introspect the program. The most common compile time variables are the
+following:
 
 =for table
     $?FILE         Which file am I in?
@@ -1152,10 +1151,13 @@ The following compile time variables allow for a deeper introspection:
     $?TABSTOP        How many spaces is a tab in a heredoc or virtual margin?
     $?NL             What a vertical newline "\n" means: LF, CR or CRLF
     $?ENC            Default encoding of various IO methods, e.g., Str.encode, Buf.decode
-    $?DISTRIBUTION   The L<Distribution|/type/Distribution> of the current compilation unit.
+    $?DISTRIBUTION   The Distribution of the current compilation unit.
 
 With particular regard to the C<$?NL>, see the  L<newline pragma|/language/pragmas>.
 
+These variables are Rakudo specific, with all the corresponding caveats:
+=for table
+$?BITS           Number of bits of the platform the program is being compiled
 
 =head3 X<&?ROUTINE>
 
@@ -1168,7 +1170,7 @@ others method related to C<Sub>:
     sub awesome-sub { say &?ROUTINE.name }
     awesome-sub # OUTPUT: awesome-sub
 
-The special variable C<&?ROUTINE> allows also for recursion:
+It also allows also for recursion:
 
 =begin code
 my $counter = 10;
@@ -1198,8 +1200,9 @@ for '.' {
 C<$?DISTRIBUTION> provides access to the L<Distribution|/type/Distribution> of
 the current compilation unit. This gives module authors a way to reference other
 files in the distribution by their original relative path names, or to view the
-metadata, without needing to know the underlying file structure (such as how
-C<CompUnit::Repository::Installation> changes the file layout on installation).
+metadata (via the C<.meta> method), without needing to know the underlying file
+structure (such as how C<CompUnit::Repository::Installation> changes the file
+layout on installation).
 
 =begin code :solo
 unit module MyFoo;