docs: update README with C API documentation

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---

Author: anandkaranubc

lib/node_modules/@stdlib/stats/base/dists/degenerate/pdf/README.md

@@ -127,6 +127,104 @@ for ( i = 0; i < 100; i++ ) {
 
 <!-- /.examples -->
 
+<!-- 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 -->
+
+<!-- C usage documentation. -->
+
+<section class="usage">
+
+### Usage
+
+```c
+#include "stdlib/stats/base/dists/degenerate/pdf.h"
+```
+
+#### stdlib_base_dists_degenerate_pdf( x, mu )
+
+Evaluates the probability density function (PDF) for a degenerate distribution centered at `mu`.
+
+```c
+double out = stdlib_base_dists_degenerate_pdf( 2.0, 3.0 );
+// returns 0.0
+```
+
+The function accepts the following arguments:
+
+-   **x**: `[in] double` input value.
+-   **mu**: `[in] double` constant value of the distribution.
+
+```c
+double stdlib_base_dists_degenerate_pdf( const double x, const double mu );
+```
+
+</section>
+
+<!-- /.usage -->
+
+<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+</section>
+
+<!-- /.notes -->
+
+<!-- C API usage examples. -->
+
+<section class="examples">
+
+### Examples
+
+```c
+#include "stdlib/stats/base/dists/degenerate/pdf.h"
+#include <stdlib.h>
+#include <stdio.h>
+
+static double random_uniform( const double min, const double max ) {
+    double v = (double)rand() / ( (double)RAND_MAX + 1.0 );
+    return min + ( v * ( max - min ) );
+}
+
+int main( void ) {
+    double x;
+    double mu;
+    double result;
+    int i;
+
+    for ( i = 0; i < 10; i++ ) {
+        x = random_uniform( -10.0, 10.0 );
+        mu = random_uniform( -20.0, 20.0 );
+        result = stdlib_base_dists_degenerate_pdf( x, mu );
+
+        printf( "x: %lf, mu: %lf, PDF: %lf \n", x, mu, result );
+    }
+
+    return 0;
+}
+```
+
+</section>
+
+<!-- /.examples -->
+
+</section>
+
+<!-- /.c -->
+
 <!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
 
 <section class="related">