Added README.

README.md

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+Vector calculation tool
+=======================
+
+This is a PHP script that creates sort of a calculation environment for working with
+vectors. Not only will it calculate various operations with vectors, it will also plot
+them, calculate angles between different vectors, intersection points, etc.
+
+Syntax
+------
+
+    set P1=[1,1,1]
+
+Sets `P1` to the vector 1, 1, 1 (x, y, z).
+
+    set P2=[2,0]
+
+Sets `P2` to the vector 2, 0(, 0).
+
+    plotL P1;P2
+
+Plots a line between vectors `P1` and `P2`.
+
+    plotdel all
+
+Removes all plots from screen.
+
+    unset P2
+
+Deletes variable `P2`.
+
+More commands are available from the onscreen help box.