docs: update README with C API documentation

---
type: pre_push_report
description: Results of running various checks prior to pushing changes.
report:
  - task: run_javascript_examples
    status: na
  - task: run_c_examples
    status: na
  - task: run_cpp_examples
    status: na
  - task: run_javascript_readme_examples
    status: na
  - task: run_c_benchmarks
    status: na
  - task: run_cpp_benchmarks
    status: na
  - task: run_fortran_benchmarks
    status: na
  - task: run_javascript_benchmarks
    status: na
  - task: run_julia_benchmarks
    status: na
  - task: run_python_benchmarks
    status: na
  - task: run_r_benchmarks
    status: na
  - task: run_javascript_tests
    status: na
---

Author: anandkaranubc

lib/node_modules/@stdlib/stats/base/dists/chisquare/mgf/README.md

@@ -151,6 +151,106 @@ for ( i = 0; i < 10; 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/chisquare/mgf.h"
+```
+
+#### stdlib_base_dists_chisquare_mgf( t, k )
+
+Evaluates the moment-generating function (MGF) for a chi-squared distribution
+* with degrees of freedom `k` at a value `t`.
+
+```c
+double out = stdlib_base_dists_chisquare_mgf( 0.4, 2.0 );
+// returns ~5.0
+```
+
+The function accepts the following arguments:
+
+-   **t**: `[in] double` input value.
+-   **k**: `[in] double` degrees of freedom (must be non-negative).
+
+```c
+double stdlib_base_dists_chisquare_mgf( const double t, const double k );
+```
+
+</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/chisquare/mgf.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 t;
+    double k;
+    double result;
+    int i;
+
+    for ( i = 0; i < 10; i++ ) {
+        t = random_uniform( -0.5, 0.4 );
+        k = random_uniform( 0.1, 10.0 );
+
+        result = stdlib_base_dists_chisquare_mgf( t, k );
+
+        printf( "t: %lf, k: %lf, MGF: %lf \n", t, k, result );
+    }
+
+    return 0;
+}
+```
+
+</section>
+
+<!-- /.examples -->
+
+</section>
+
+<!-- /.c -->
+
 <!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="references">