CONTRIBUTING.md: fix consistency

Use the same capitalisation with Open Source Software

.github/CONTRIBUTING.md

@@ -17,7 +17,7 @@ We're trying to keep it simple and promote the best tools, not all of them.
 - Easy to use. Could your mother use that tool or service? Usability is most important.
 - Cross-platform / Accessible.
 - Privacy respecting.
-- Open Source / free software is preferred but not required.
+- Open Source / Free Software is preferred but not required.
 - Must list source code in [source_code.md](https://github.com/privacytoolsIO/privacytools.io/blob/master/source_code.md) (if applicable)
 - Prioritize Products without Vendor Lock-in (decentralized/self-hostable) or data interoperability.
 
@@ -37,7 +37,7 @@ Note: This criteria applies to all of privacytools.io
 ### VPN
 - Prioritize Products by privacy respecting nationality.
 - Cannot be based in USA or UK.
-- Must be acessable via open source software (i.e OpenVPN, WireGuard)
+- Must be acessable via Open Source Software (i.e OpenVPN, WireGuard)
 - Use Encryption
 - Accept Cryptocurrency
 - No logging policy
@@ -45,7 +45,7 @@ Note: This criteria applies to all of privacytools.io
 ### Email
 - Outside of USA
 - Support SMTP SSL
-- Accessable Using Open source Software (i.e IMAP)
+- Accessable Using Open Source Software (i.e IMAP)
 
 ### Hardware
 - Must be [H-Node Class A](https://h-node.org/wiki/page/en/compatibility-classes) or Equivlant (if applicable)
@@ -54,7 +54,7 @@ Note: This criteria applies to all of privacytools.io
 
 ### Software
 - Must be able to download over encrypted network (can be a mirror)
-- Must be open source software
+- Must be Open Source Software
 
 ### Encryption
 - Only verifiable encryption is to be trusted