add 'experimental' mention to the circom frontend

src/README.md

@@ -32,4 +32,4 @@ Work in progress:
 Available frontends to define the folded circuit:
 
 - [arkworks](https://github.com/arkworks-rs), arkworks contributors
-- [Circom](https://github.com/iden3/circom), iden3, 0Kims Association
+- [Circom](https://github.com/iden3/circom), iden3, 0Kims Association. Experimental frontend using [arkworks/circom-compat](https://github.com/arkworks-rs/circom-compat).

src/usage/frontend-circom.md

@@ -1,4 +1,6 @@
 # Circom frontend
+ > Experimental frontend using [arkworks/circom-compat](https://github.com/arkworks-rs/circom-compat).
+ 
 We can define the circuit to be folded in Circom. The only interface that we need to fit in is:
 
 ```c

src/usage/frontend.md

@@ -1,6 +1,6 @@
 # Frontend
 
-The frontend interface allows to define the circuit to be folded. The currently available frontends are [`circom`](https://github.com/iden3/circom) and [arkworks](https://github.com/arkworks-rs/r1cs-std). We will show here how to define a circuit using `arkworks`.
+The frontend interface allows to define the circuit to be folded. The currently available frontends are [circom](https://github.com/iden3/circom) and [arkworks](https://github.com/arkworks-rs/r1cs-std). We will show here how to define a circuit using `arkworks`.
 
 # The `FCircuit` trait