docs: Create glossary (#92)

* docs: Create glossary and update _toc.yml file

* style: pre-commit fixes

* docs: Add glossary title

* docs: updated Glossary

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/source/_toc.yml

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   - file: citation
   - file: license
   - file: modules
+  - file: glossary

docs/source/glossary.rst

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+Glossary
+========
+
+arcsec
+------
+    Arcsecond, a unit of angular measurement equal to 1/3600 of a degree. Used here to denote coordinates in the lens plane, deflection angles, the core radius, the scale radius, the Einstein radius of the lens, and the softening parameter.
+
+
+arcsec^2
+--------
+    Square arcseconds, used to denote the gravitational lensing potential at given coordinates and also used in the calculation of the radius in the lensing potential and convergence formulas.
+
+
+Msun
+----
+    Solar mass, used here to denote the total mass of the lens.
+
+
+Mpc
+---
+    Megaparsec, a unit of distance used in astronomy, used to denote distances related to the angular diameter distance in the cosmology calculations.
+
+
+Msun/Mpc^2
+----------
+    Solar masses per square megaparsec, used to denote the surface mass density at given coordinates and the critical surface density.
+
+
+Msun/Mpc^3
+----------
+    Solar masses per cubic megaparsec, used here to denote the central mass density in the central convergence calculation.
+
+
+seconds
+-------
+    Time unit, used here to denote the gravitational time delay.
+
+
+radians
+-------
+    A unit of angular measure used to denote the orientation of the lens on the sky and the position angle of the lens.
+
+meters
+------
+    A unit of length in the metric system, used here to denote the position vector in the lens plane in the EPL model.
+
+
+arcsec/pixel
+------------
+    Arcseconds per pixel, used to denote the pixel scale of the source image in the lens plane, indicating the angular size each pixel represents.
+
+
+flux
+----
+    A unit of brightness, used here to denote the intensity values within the pixelated source image and the intensity at the effective radius (Ie) of the Sersic source.
+
+
+unitless
+--------
+    Indicates a dimensionless quantity, used here for redshifts, the axis ratio of the lens, the power-law slope parameter of the lens model, shear components, the redshift of the lens, the concentration parameter, and the convergence of the lens.