[doc] include single bar legend style

Author: praffeck

doc/latex/pgfplots/pgfplots.reference.axisdescription.tex

@@ -1607,7 +1607,7 @@ \subsection{Legend Appearance}
 \end{codeexample}
 \end{stylekey}
 
-\begin{pgfplotsxykeylist}{\x bar legend,\x bar interval legend}
+\begin{pgfplotsxykeylist}{\x bar legend,\x bar interval legend,single \x bar legend}
     These style keys redefine |legend image code| such that legends use |xbar|,
     |ybar| or the |xbar interval| and |ybar interval| handlers.
     %
@@ -1658,6 +1658,18 @@ \subsection{Legend Appearance}
             plot coordinates {(0cm,0.8em) (5pt,0.6em) (10pt,0.6em)};
         },
     },
+    /pgfplots/single xbar legend/.style={
+        /pgfplots/legend image code/.code={
+            \draw[##1,/tikz/.cd,bar width=6pt,yshift=0.2ex,bar shift=0pt]
+            plot coordinates {(0.8em,0pt)};
+        },
+    },
+    /pgfplots/single ybar legend/.style={
+        /pgfplots/legend image code/.code={
+            \draw[##1,/tikz/.cd,bar width=6pt,yshift=-0.2em,bar shift=0pt]
+            plot coordinates {(0pt,0.8em)};
+        },
+    },
 }
 \end{codeexample}
 \end{pgfplotsxykeylist}