Add ZSTD_getDictID_fromCDict function to experimental section

doc/zstd_manual.html

@@ -1158,6 +1158,12 @@ static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL };  </b>/**< t
   note: equivalent to ZSTD_createCDict_advanced(), with dictLoadMethod==ZSTD_dlm_byRef 
 </p></pre><BR>
 
+<pre><b>unsigned ZSTD_getDictID_fromCDict(const ZSTD_CDict* cdict);
+</b><p>  Provides the dictID of the dictionary loaded into `cdict`.
+  If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
+  Non-conformant dictionaries can still be loaded, but as content-only dictionaries. 
+</p></pre><BR>
+
 <pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
 </b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
  `estimatedSrcSize` value is optional, select 0 if not known