docs: Adding information about the masks used in SKY130.

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>
diff --git a/docs/rules.rst b/docs/rules.rst
index bd1d5bd..32ad1c2 100644
--- a/docs/rules.rst
+++ b/docs/rules.rst
@@ -7,6 +7,7 @@
     :maxdepth: 2
 
     rules/background
+    rules/masks
     rules/assumptions
     rules/periphery
     rules/errors
diff --git a/docs/rules/masks.csv b/docs/rules/masks.csv
new file mode 100644
index 0000000..9635d71
--- /dev/null
+++ b/docs/rules/masks.csv
@@ -0,0 +1,52 @@
+Mask,Acronym,Used in SKY130

+Field Oxide,FOM,X

+Deep N-Well,DNM,X

+P-Well Block Mask,PWBM,

+P-Well Drain Extended ,PWDEM,

+N-Well*,NWM,X

+High Vt PCh*,HVTPM,X

+Low Vt Nch*,LVTNM,X

+HLow VT PCh Radio*,HVTRM,X

+N-Core Implant,NCM,

+Tunnel Mask,TUNM,X

+ONO Mask,ONOM,X

+Low Voltage Oxide,LVOM,X

+Resistor Protect,RPM,X

+Poly 1,P1M,X

+N-tip Implant,NTM,X

+High Volt. N-tip,HVNTM,X

+Lightly Doped N-tip,LDNTM,X

+Nitride Poly Cut,NPCM,X

+P+ Implant,PSDM,X

+N+ Implant,NSDM,X

+Local Intr Cont.1,LICM1,X

+Local Intrcnct 1,LI1M,X

+Contact,CTM1,X

+Open Frame Mask,OFM,

+Metal 1,MM1,X

+Via,VIM,X

+Capacitor MiM,CAPM,

+Metal 2,MM2,X

+Via 2-TNV,VIM2,

+Via 2-S8TM,VIM2,

+Via 2-PLM,VIM2,X

+Metal 3-TLM,MM3,

+Metal 3-S8TM,MM3,

+Metal 3-PLM,MM3,X

+Pad Via,VIPDM,

+Via3-PLM,VIM3,X

+Inductor-TLM,INDM,

+Metal 4,MM4,X

+Via4,VIM4,X

+Metal 5,MM5,X

+Nitride Seal Mask,NSM,X

+Pad (scribe protect),PDM,X

+Pad (scribe unprotect),PDM,

+Polyimide,PMM,

+Polyimide_ExtFab,PMM[E],

+Pad&Polyimide_ExtFab,PDMM[E],

+DECA PBO,PBO,X

+Cu Inductor/Redist.,CU1M,X

+Polyimide 2 (2),PMM2,X

+Under Bump Metal,UBM,

+Bumps,BUMP,

diff --git a/docs/rules/masks.rst b/docs/rules/masks.rst
new file mode 100644
index 0000000..49124b1
--- /dev/null
+++ b/docs/rules/masks.rst
@@ -0,0 +1,14 @@
+Masks
+=====
+
+The :download:`masks.csv file <./masks.csv>` provides a raw information for the
+mask layers (name, acronym, usage) currently used found on 130nm processes at
+SkyWater.
+
+The masks which are used on the SKY130 technology node (that this PDK supports)
+are marked.
+
+.. csv-table:: Table - Masks
+   :file: masks.csv
+   :header-rows: 1
+   :widths: 70, 20, 10