docs: add bson_string_truncate(3)
docs: add bson_string_truncate(3)

remicollet/libbson,rcsanchez97/libbson,Convey-Compliance/libbson,rayyang2000/libbson,remicollet/libbson,mongodbinc-interns/libbson,paulmelnikow/libbson,derickr/libbson,rayyang2000/libbson,4Second2None/libbson_tmp,mapr/libbson,Machyne/libbson,paulmelnikow/libbson,mongodbinc-interns/libbson,jqk6/libbson,bjori/libbson,derickr/libbson,mongodb/libbson,bjori/libbson,mongodbinc-interns/libbson,Machyne/libbson,alexeyvo/libbson,4Second2None/libbson_tmp,rayyang2000/libbson,jqk6/libbson,jqk6/libbson,paulmelnikow/libbson,bjori/libbson,ksuarz/libbson,Machyne/libbson,4Second2None/libbson_tmp,paulmelnikow/libbson,paulmelnikow/libbson,remicollet/libbson,rcsanchez97/libbson,Convey-Compliance/libbson,mapr/libbson,jqk6/libbson,mongodb/libbson,rayyang2000/libbson,ksuarz/libbson,mongodb/libbson,alexeyvo/libbson,Convey-Compliance/libbson,rcsanchez97/libbson,mongodbinc-interns/libbson,derickr/libbson,mapr/libbson,alexeyvo/libbson,ajdavis/libbson,remicollet/libbson,Machyne/libbson,4Second2None/libbson_tmp,derickr/libbson,ksuarz/libbson,ajdavis/libbson,ajdavis/libbson