add a note about forking the repo in README.md (#52)

.gitignore

@@ -28,3 +28,4 @@ whitelist.json
 src/main/resources/mixins.*.json
 *.bat
 layout.json
+.DS_Store

README.md

@@ -0,0 +1,13 @@
+# Waila
+
+## Contribution
+
+When forking this repository, make sure to uncheck the `Copy the master branch only` option.
+This will copy all tags to your fork, so the build system can detect the latest mod version.
+If you leave it checked, you won't be able to enter the world in a local client run because Waila [will think the mod is outdated](https://github.com/GTNewHorizons/waila/blob/master/src/main/java/mcp/mobius/waila/Waila.java#L133).
+
+If you already forked the repository without tags, you can fetch them manually:
+```
+git remote add upstream https://github.com/GTNewHorizons/waila
+git fetch upstream --tags
+```

src/main/java/mcp/mobius/waila/api/IWailaVariableWidthTooltipRenderer.java

@@ -1,5 +1,7 @@
 package mcp.mobius.waila.api;
 
+import java.awt.Dimension;
+
 /**
  * Interface for tooltip renderers that adjust their width depending on the width of the rest of the tooltip.
  * setMaxLineWidth is called by {@link mcp.mobius.waila.overlay.Tooltip} before every tooltip render to inform the
@@ -7,6 +9,17 @@ package mcp.mobius.waila.api;
  */
 public interface IWailaVariableWidthTooltipRenderer extends IWailaTooltipRenderer {
 
+    /**
+     * Return the size of the tooltip. for variable width renderers it is recommended to return the minimum width needed
+     * for the line, then draw the actual width using getMaxLineWidth(). They do not need to actually match.
+     *
+     * @param params   Array of string parameters as passed to the RENDER arg in the tooltip
+     *                 ({rendername,param1,param2,...})
+     * @param accessor A global accessor for TileEntities and Entities
+     * @return Dimension of the reserved area
+     */
+    Dimension getSize(String[] params, IWailaCommonAccessor accessor);
+
     /**
      * Informs the renderer of what the length of the longest line is.</br>
      * Called by {@link mcp.mobius.waila.overlay.Tooltip} before every tooltip render.</br>