Add SAGE to doc (#330)

Author: blegat

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
 #            os: ubuntu-latest
 #            arch: x64
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}
@@ -45,6 +45,6 @@ jobs:
         with:
           depwarn: error
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v1
+      - uses: codecov/codecov-action@v3
         with:
           file: lcov.info

docs/src/constraints.md

@@ -360,6 +360,24 @@ PolyJuMP.Bridges.Objective.ToPolynomialBridge
 PolyJuMP.Bridges.Constraint.ToPolynomialBridge
 ```
 
+### SAGE extension
+
+To use the SAGE cone in place of the Sum-of-Squares cone for an inequality constraints
+between polynomials, use the following:
+```julia
+import PolyJuMP
+PolyJuMP.setpolymodule!(model, PolyJuMP.SAGE)
+```
+
+```@docs
+SumOfSquares.PolyJuMP.SAGE.Polynomials
+SumOfSquares.PolyJuMP.SAGE.Decomposition
+SumOfSquares.PolyJuMP.SAGE.Signomials
+SumOfSquares.PolyJuMP.SAGE.DecompositionAttribute
+SumOfSquares.PolyJuMP.SAGE.SignomialsBridge
+SumOfSquares.PolyJuMP.SAGE.AGEBridge
+```
+
 ### Internal functions
 
 ```@docs