Added README.

README.md

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+# OMF
+
+A library for reading a writing files in Open Mining Format 2.0.
+
+## What is OMF
+
+OMF is an open-source serialization format and library to support data interchange
+across the entire mining community.
+Its goal is to standardize file formats and promote collaboration.
+
+This repository provides a file format specification and a Rust library for reading and writing files,
+plus a wrapper to use that library from C.
+
+## What OMF Stores
+
+### Elements
+
+- Points.
+- Line segments.
+- Triangulated surfaces.
+- Grid surfaces.
+    - Regular or tensor grid spacing.
+    - Any orientation.
+- Block models, with optional sub-blocks.
+    - Regular or tensor grid spacing.
+    - Any orientation.
+    - Regular sub-blocks that lie on a grid within their parent, with octree or arbitrary layout.
+    - Free-form sub-blocks that don't lie on any grid.
+- Composite elements made out of any of the above.
+
+### Attributes
+
+- Floating-point or signed integer values.
+- Date and date-time values.
+- Category values, storing an index used to look up name, color, or other sub-attributes.
+- Boolean or filter values.
+- 2D and 3D vectors.
+- Text values.
+- Color values.
+- Projected texture images.
+- UV mapped texture images.
+
+Attributes values can be valid or null.
+They can be attached to different parts of each element type,
+such as the vertices vs. faces of a surface,
+or the parent blocks vs. sub-blocks of a block model.