I'm new in the tikz environment and I would like to put an arrow head in the middle of the black line. I would like someone to tell me how can I do this or where I can learn how to do it, because I've been looking and the tikz manual https://www.bu.edu/math/files/2013/08/tikzpgfmanual.pdf doesn't seems to say anything explicit about this. The code is
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{babel}
\usetikzlibrary {intersections}
\usetikzlibrary {arrows.meta}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[scale=2, >=Stealth]
\draw (-0.3,0) -- (1.5,0) node[anchor=north, pos=0.95]{$\vec{\boldsymbol{x}}$};
\draw (0,-0.3) -- (0,1.5) node[anchor=north east]{$t$};
\draw [very thick] (0.3,0.3) -- node[anchor = north, pos = -0.05]{$x$} (1.2,1.2) node[anchor = north, pos = 1.2]{$y$};
\filldraw [black] (0.3,0.3) circle [radius=1pt]
(1.2,1.2) circle [radius=1pt];
\end{tikzpicture}
\end{document}
Here's the output
