Update README.md

README.md

@@ -13,6 +13,7 @@ A collection of random crackme and programming puzzle solutions created using **
 * [TLOD's Easy Crackme solution](https://github.com/Marco888Space/Reverse-Engineering-crackmes-with-Ghidra/blob/main/solutions/crackme_1/crackme_1_solution.md)
 * [RedXen's C File CrackMe solution](https://github.com/Marco888Space/Reverse-Engineering-crackmes-with-Ghidra/blob/main/solutions/crackme_2/crackme_2_solution.md)
 * [Danofred's KeygenMe - 01 (update) solution](https://github.com/Marco888Space/Reverse-Engineering-crackmes-with-Ghidra/blob/main/solutions/crackme_3/crackme_3_solution.md)
+* [psyr3n's PIDXploit solution](https://github.com/QuantumWizard888/Reverse-Engineering-crackmes-with-Ghidra/blob/main/solutions/crackme_4/crackme_4_solution.md)
 
 ## === Resources === ##
 * **Ghidra**: https://github.com/NationalSecurityAgency/ghidra/