docs: fix incorrect structure in READMEs of blas/ext/base/*

PR-URL: #5163
Ref: #5151
Co-authored-by: Athan Reines <[email protected]>
Reviewed-by: Athan Reines <[email protected]>

Author: aayush0325

lib/node_modules/@stdlib/blas/ext/base/cfill/README.md

@@ -259,11 +259,11 @@ console.log( x.get( 0 ).toString() );
 
 <!-- /.examples -->
 
-<!-- C interface documentation >
+<!-- C interface documentation. -->
 
 * * *
 
-<section class="C">
+<section class="c">
 
 ## C APIs
 

lib/node_modules/@stdlib/blas/ext/base/dsortins/README.md

@@ -148,12 +148,18 @@ console.log( x );
 
 <!-- /.examples -->
 
-<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
-
-<section class="related">
+<!-- C interface documentation. -->
 
 * * *
 
+<section class="c">
+
+## C APIs
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
 </section>
 
 <!-- /.intro -->
@@ -265,6 +271,10 @@ int main( void ) {
 
 <!-- /.c -->
 
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
 ## See Also
 
 -   <span class="package-name">[`@stdlib/blas/ext/base/dsort2ins`][@stdlib/blas/ext/base/dsort2ins]</span><span class="delimiter">: </span><span class="description">simultaneously sort two double-precision floating-point strided arrays based on the sort order of the first array using insertion sort.</span>

lib/node_modules/@stdlib/blas/ext/base/zfill/README.md

@@ -259,11 +259,11 @@ console.log( x.get( 0 ).toString() );
 
 <!-- /.examples -->
 
-<!-- C interface documentation >
+<!-- C interface documentation. -->
 
 * * *
 
-<section class="C">
+<section class="c">
 
 ## C APIs