Adding documentation

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+.. _updatewcs:
+
+**************************************
+UPDATEWCS
+**************************************
+UPDATEWCS applies corrections to the WCS of a science file
+and adds reference information as header keywords and fits 
+file extensions so that a science file contains all necessary 
+information to represent astrometrically precise positions.
+The order in which the corrections are applied is important 
+and is as follows:
+
+- Detector to Image Correction
+
+- Apply Time dependent distortion (if applciable)
+
+- Recomputing the basic WCS
+
+- Apply Velocity Aberration Correction
+
+- Apply polynomial distortion through the SIP coefficients
+
+- Apply non-polynomial distortion
+
+Mathematicall the entire transformation from detector to sky 
+coordinates is described by:
+
+.. math:: (x',y') &= DET2IM(x,y) 
+
+.. math:: \binom{u'}{v'} &= \binom{x' - CRPIX1}{y' - CRPIX2}
+
+.. math:: \left( \begin{array}{ll}
+         \alpha \\
+         \delta \\
+         \end{array} \right) &=
+      \left( \begin{array}{ll}
+      CRVAL1 \\
+      CRVAL2\\
+      \end{array} \right) + 
+      \left( \begin{array}{cc}
+      CD11 & CD12 \\ 
+      CD21 & CD22\\
+      \end{array} \right) 
+      \left( \begin{array}{ll}
+      u' + f(u',v') + LT_x(x',y') \\ 
+      v' + g(u',v') + LT_y(x',y') \\ 
+      \end{array} \right)
+    
+where f(u',v') and g(u',v') represent the polynomial distortion correction specified as
+
+.. math:: f(u',v') = \sum_{p+q=2}^{AORDER} A_{pq} {u'}^{p} {v'}^{q}
+          \\
+          g(u',v')  = \sum_{p+q=2}^{BORDER} B_{pq} {u'}^{p} {v'}^{q}
+
+
+where
+
+* x', y' are the initial coordinates x,y with the 68th column correction applied through the DET2IM convention
+* u',v' are the DET2IM-corrected coordinates relative to CRPIX1,CRPIX2
+* LT<sub>x</sub>, LT<sub>y</sub> is the residual distortion in the lookup tables written to the header using the Paper IV lookup table convention
+* A, B are the SIP coefficients specified using the SIP convention
+
+.. toctree::
+   :maxdepth: 2
+   
+   updatewcs_ui
+   apply_corrections
+   wcs_corrections
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